ISO/FDIS 8434-2

• Abstract:

  ISO 8434-2:2007 specifies general and dimensional requirements for the design and performance of 37° flared connectors that are suitable for use with ferrous and non-ferrous tubes with outside diameters from 6 mm to 50,8 mm, inclusive. These connectors are for use in fluid power and general applications within the limits of pressure and temperature specified. They are intended for the connection of tubes and hose fittings to ports in accordance with ISO 6149‑1, ISO 1179‑1, ISO 9974‑1 and ISO 11926‑1. (See ISO 12151‑5 for related hose fitting specification.) ISO 8434-2:2007 also specifies a performance and qualification test for 37° flared connectors.

• Status: Not Published
• ICS: 23.100.40 - Piping and couplings
• Technical Committee: ISO/TC 131/SC 4 - Connectors and similar products and components
• Drafting Committee: ISO/TC 131/SC 4/WG 6 - Methods for connecting hose fittings and tubes to connectors
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 10-Sep-2026
• Completion Date: 10-Sep-2026

• Revises: ISO 8434-2:2007 - Metallic tube connections for fluid power and general use — Part 2: 37 degree flared connectors
• Effective Date: 16-Dec-2023

Overview

ISO/FDIS 8434-2:2026, developed by the International Organization for Standardization (ISO), defines the requirements for 37° flared metallic tube connectors used in fluid power and general applications. This standard applies to connectors suitable for ferrous and non-ferrous tubes with outside diameters from 4 mm to 50.8 mm. These 37° flared connectors are essential for creating reliable, leak-free joints in hydraulic and pneumatic systems, and are widely recognized for use with both metric and inch-sized tubes.

The standard provides comprehensive guidance on connector design, performance, materials, assembly, and qualification testing, ensuring compatibility and interchangeability for fluid power applications across the globe.

Key Topics

• Scope of Applicability:
  • Covers flared connectors for tubes and hose fittings, suitable for a range of tube sizes and materials.
  • Applicable across both hydraulic and pneumatic systems in industrial and general settings.
• Material Requirements:
  • Connectors are made from carbon steel or stainless steel to ensure durability and corrosion resistance.
  • Nuts and sleeves must match connector body materials for proper function and longevity.
• Pressure and Temperature Ratings:
  • Specifies working pressures and temperature limits based on tube and connector material.
  • Ensures connectors operate reliably under defined environmental conditions.
• Dimensional and Performance Standards:
  • Details on external and internal dimensions, including across-flats and wall thickness requirements.
  • Metal-to-metal sealing design provides full-flow connections with robust performance.
• Assembly and Identification:
  • Provides standardized connector designation system for efficient ordering and identification.
  • Outlines marking, assembly instructions, and procurement information.

Applications

ISO/FDIS 8434-2 37° flared connectors are integral to a wide array of fluid power and general industrial systems, offering robust, leak-free connections for rigid and flexible tubing. Key application areas include:

• Industrial Hydraulic Systems: Used in machinery for manufacturing, construction, and material handling, where high-pressure, reliable connections are essential.
• Mobile Equipment: Essential in vehicles such as excavators, cranes, and agricultural equipment for transmitting hydraulic power.
• General Pneumatic Applications: Applied in compressed air systems for automation and control equipment.
• Process Industries: Utilized in chemical, petrochemical, and refining industries for secure fluid transport.
• Marine and Aerospace: Provides corrosion-resistant, high-performance tube connections in demanding environments.

The standard ensures these connectors are interchangeable with ports in accordance with widely adopted ISO port standards, such as ISO 6149-1, ISO 1179-1, ISO 9974-1, and ISO 11926-1.

Related Standards

ISO/FDIS 8434-2 is part of a broader suite of international standards, helping maintain quality, interchangeability, and safety in fluid power systems. Related standards include:

• ISO 6149-1: Ports and stud ends with ISO metric threads and O-ring sealing, for general and fluid power use.
• ISO 1179-1: Ports and stud ends with ISO 228-1 threads with metal-to-metal or elastomeric sealing.
• ISO 9974-1: Ports and stud ends with ISO 261 threads for general and fluid power applications.
• ISO 11926-1: Ports and stud ends with ISO inch screw threads and O-ring sealing.
• ISO 12151-5: Hose fittings for 37° flared connectors.
• ISO 1127: Stainless steel tube dimensions and tolerances.
• ISO 19879: Test methods for metallic tube connections.

For optimal compatibility and safety, users and manufacturers should consult these related standards when designing or specifying fluid power systems.

Keywords: ISO 8434-2, 37° flared connectors, fluid power connectors, hydraulic tube fittings, metallic tube connections, international standards, hydraulic connectors, pneumatic connectors, tube assembly, ISO 6149, ISO 1179, industrial fittings.

FINAL DRAFT
International
Standard
ISO/TC 131/SC 4
Metallic tube connections for fluid
Secretariat: ANSI
power and general use —
Voting begins on:
2026-09-10
Part 2:
37 degree flared connectors
Voting terminates on:
2026-11-05
Raccordements de tubes métalliques pour transmissions
hydrauliques et pneumatiques et applications générales —
Partie 2: Connecteurs évasés à 37 degrés
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 131/SC 4
Metallic tube connections for fluid
Secretariat: ANSI
power and general use —
Voting begins on:
Part 2:
37 degree flared connectors
Voting terminates on:
Raccordements de tubes métalliques pour transmissions
hydrauliques et pneumatiques et applications générales —
Partie 2: Connecteurs évasés à 37 degrés
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
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Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Materials . 3
4.1 General .3
4.2 Connector bodies .3
4.3 Nuts . .3
4.4 Sleeves .4
5 Pressure and temperature requirements . 4
6 Designation of connectors . 5
7 Requirements for tubes . 7
8 Across flats dimensions and tolerances . 9
9 Design .10
9.1 Connectors .10
9.2 Dimensions .10
9.3 Passage tolerances .10
9.4 Wall thickness .10
9.5 Angular tolerances .10
9.6 Contour details .10
9.7 Stud ends . .10
9.8 Reducing connectors .10
10 Screw threads .11
10.1 37° flared ends.11
10.2 Stud ends (connection ends) .11
11 Manufacture .11
11.1 Construction .11
11.2 Workmanship .11
11.3 Corrosion protection .11
11.4 Connector protection . . 12
11.5 Corners . 12
12 Assembly instructions .12
13 Procurement information .12
14 Marking of components .13
15 Performance and qualification test .13
15.1 Performance requirements . 13
15.1.1 Proof test . 13
15.1.2 Burst test . 13
15.1.3 Cyclic endurance (impulse) test .14
15.1.4 Overtightening test .14
15.1.5 Repeated assembly test .14
16 Identification statement .15
Annex A (normative) Length reduction factors for reducing connectors .46
Bibliography .54

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee SC 4,
Connectors and similar products and components.
This third edition cancels and replaces the second edition (ISO 8434-2:2007), which has been technically
revised.
The main changes are as follows:
— Introduction and Clause 10, ISO 263 cross-references replaced with ISO 725.
— Clause 1 “Scope” updated to include tubes with outside diameters from 4 mm to 50,8 mm. Sizes 4, 5, and
22 mm have been added to all applicable tables.
— Clause 2 “Normative references” updated.
— Clause 3 “Terms and definitions” updated. Figure 1 added.
— 4.2, removed all references to connector bodies made from copper alloys.
— 5.3, removed pressure derating for connectors made from stainless steel.
— 6.7, added material and letter designations.
— Clause 7 “Requirements for tubes” rewritten to remove references to ISO 3304 and ISO 3305.
— 8.1, added forging size criteria.
— 9.4 “Wall Thickness” added.
— Clause 10 “Screw Threads” rewritten.
— 11.3 “Corrosion protection” rewritten.
— Clause 12 “Assembly Instructions” rewritten.

iv
— Clause 13 “Procurement information” seal material added.
— 15.1 “Performance requirements” rewritten.
— 15.1.5 “Repeated assembly test” added, “Re-use of test samples” removed.
— Clause 16 “Identification statement” rewritten.
— All figures have been renumbered and redrawn.
— Figure 5, tolerance added to R0,5 radius.
— Figure 7 and Table 8 were added for the recommended chamfer for single flares.
a
— Table 9, footnote “ ” added.
— Figure 10, R0,26 ± 0,13 changed to R0,25 ± 0,15.
— Figure 11/Table 12, added “L ” dimension and subsequent “L” dimensions were adjusted in following
figures and tables.
— Table 13, removed Tube OD 50.
— Figure 18/Table 19 and Figure 19/Table 20, Optional dual angle seat design added.
— Figure 19/Table 20 added “L ”.
— Table A.3 factor for 9/16-18 and 16 updated to -0,4.
— Bibliography updated.
A list of all parts in the ISO 8434 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
Introduction
In fluid power systems, power is transmitted and controlled through a fluid (liquid or gas) under pressure
within an enclosed circuit. In general applications, a fluid may be conveyed under pressure.
Components may be connected through their ports by connections (connectors), tubes and hoses. Tubes are
rigid conductors; hoses are flexible conductors.
[1] [2]
This document is based on the US standard SAE J514-1 and SAE J533 . The threads for the 37° flared
connection are unified inch threads in accordance with ISO 725. The inch threads were not changed to
metric threads according to ISO 261 to allow connectors complying with this document to be used in existing
applications without requiring a change to tube or hose assemblies. Also, the thread-to-nut overtightening
and seal performance have been extensively tested; to change to metric threads would require an extensive
test program at considerable cost without providing any functional improvement. The threads are integral to
themselves, connectors of this type match only to themselves and, other than having metric threads, no value
in changing could be found. Major international companies that have used these connectors have adopted
the design without noting any problems. All wrench flats specified in this document are dimensioned to be
used with ISO standard metric wrenches.

vi
FINAL DRAFT International Standard ISO/FDIS 8434-2:2026(en)
Metallic tube connections for fluid power and general use —
Part 2:
37 degree flared connectors
1 Scope
This document specifies the general and dimensional requirements for the design and performance of
37° flared connectors that are suitable for use with ferrous and non-ferrous tubes with outside diameters
from 4 mm to 50,8 mm, inclusive. These connectors provide full-flow connections with metal-to-metal
sealings. These connectors are for use in fluid power and general applications within the limits of pressure
and temperature specified in this document.
They are intended for the connection of tubes and hose fittings to ports in accordance with ISO 6149-1,
ISO 1179-1, ISO 9974-1 and ISO 11926-1. (See ISO 12151-5 for related hose fitting specification.)
NOTE 1 For new designs in hydraulic fluid power applications, see the requirements given in 9.7. Where the
requirements of the application allow for the use of elastomeric seals, connector designs that conform to International
Standards and incorporate elastomeric sealing are preferred.
NOTE 2 For use under conditions outside the limits for pressure or temperature, or both, see 5.4.
Both metric and inch tubing can be accommodated by changing the sleeve (see Figure 9). In the past, these
connectors have been used predominantly with inch tubing. For new and future designs, the use of metric
tubing is preferred.
This document also specifies performance and qualification tests for 37° flared connectors.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 725, ISO inch screw threads — Basic dimensions
ISO 1127, Stainless steel tubes — Dimensions, tolerances and conventional masses per unit length
ISO 1179-3, Connections for general use and fluid power — Ports and stud ends with ISO 228-1 threads with
elastomeric or metal-to-metal sealing — Part 3: Light-duty (L series) stud ends with sealing by O-ring with
retaining ring (types G and H)
ISO 4759-1, Tolerances for fasteners — Part 1: Bolts, screws, studs and nuts — Product grades A, B and C
ISO 5598, Fluid power systems and components — Vocabulary
ISO 6149-3, Connections for hydraulic fluid power and general use — Ports and stud ends with ISO 261 metric
threads and O-ring sealing — Part 3: Dimensions, design, test methods and requirements for light-duty (L series)
stud ends
ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests
ISO 9974-2, Connections for general use and fluid power — Ports and stud ends with ISO 261 threads with
elastomeric or metal-to-metal sealing — Part 2: Stud ends with elastomeric sealing (type E)

ISO 11926-3, Connections for general use and fluid power — Ports and stud ends with ISO 725 threads and
O-ring sealing — Part 3: Light-duty (L series) stud ends
ISO 19879, Metallic tube connections for fluid power and general use — Test methods for hydraulic fluid power
connections
ISO 21920-1, Geometrical product specifications (GPS) — Surface texture: Profile — Part 1: Indication of surface
texture
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5598 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
adjustable stud end
stud end connector that allows for connector orientation through final tightening of the locknut to complete
the connection
Note 1 to entry: This type of stud end is typically used on shaped connectors (e.g. tees, crosses and elbows).
3.2
non-adjustable stud end
stud end connector that does not require specific orientation before final tightening of the connection
because it is only used on straight connectors
3.3
run
two principal, axially aligned outlets of a tee connector or cross connector
Key
1 run
2 branch
Figure 1 — Run and branch illustration
3.4
branch
side outlet(s) of a tee connector or cross connector
3.5
chamfer
removal of a conical portion at the entrance of a thread to assist assembly and prevent damage to the start
of the thread
3.6
assembly torque
torque required to achieve a satisfactory final connection

3.7
qualification test torque
torque used to verify conformity of the connector to the requirements of this document
3.8
overtightening
torque that the nut withstands without deformation that renders it unusable
3.9
jump size connector
connector with dis-similar end connections, for example, –6 male flare with a –12 stud end
4 Materials
4.1 General
Figure 2 shows the cross-section and components of a typical 37° flared connector.
Key
1 straight stud connector body
2 tube nut
3 tube
4 sleeve
5 O-ring
a
Stud end in accordance with ISO 1179-3, ISO 6149-3, ISO 9974-2 or ISO 11926-3.
Figure 2 — Cross-section of typical 37° flared connection
4.2 Connector bodies
Bodies shall be manufactured from carbon steel or stainless steel, which will provide the minimum
requirements for the pressure and temperature ratings specified in Clause 5 when tested in accordance
with Clause 15. They shall have characteristics that make them suitable for use with the fluid to be conveyed
and to provide an effective joint.
4.3 Nuts
Nuts to be used with carbon steel bodies shall be made of carbon steel and those for use with stainless steel
bodies shall be made of stainless steel unless otherwise specified.

4.4 Sleeves
Sleeves shall be manufactured from a material similar to the bodies.
5 Pressure and temperature requirements
5.1 The working pressure of the connector shall be the lower of the working pressure of the 37° flared
connector connection given in Table 1 and the working pressure of the respective stud end.
5.2 Flared connectors in accordance with this document made of carbon steel shall meet or exceed without
leakage the requirements to the working pressures given in Table 1 when used at temperatures from −40 °C
to +120 °C with petroleum base hydraulic fluids.
5.3 Connectors made of stainless steel complying with this document shall be suitable for use at the
working pressures given in Table 1 when used at temperatures from −60 °C to +50 °C.
5.4 For applications under conditions outside the limits for pressure or temperature, or both given in
Table 1 and in 5.2 and 5.3, the manufacturer shall be consulted.
5.5 Connectors conforming to this document shall be tested in accordance with Clause 15 to ensure that
they meet or exceed the pressure requirements given in Table 1.
5.6 The pressure and temperature requirements given in Table 1 and in 5.2 and 5.3 are for tube
connections and connector bodies only. For port and stud end pressure and temperature ratings, the values
in the respective port and stud end standards shall apply.
5.7 To achieve these maximum working pressures with a 4:1 design factor, the maximum tube wall
thicknesses shown in Table 1 are sufficient. See ISO 10763 to confirm the necessary tube wall thickness for a
specific working pressure.
Table 1 — Working pressures for 37° flared connections
Maximum wall thickness of
b
Tube outside diameter (OD) Maximum working pressure
a
tube for flaring
Metric Inch Metric tube Inch tube Carbon steel and stainless steel
c
mm in mm mm MPa (bar)
4 1/8 1 0,89 35 (350)
5 3/16 1 0,89 35 (350)
6 1/4 1,5 1,65 35 (350)
8 5/16 1,5 1,65 35 (350)
10 3/8 1,5 1,65 35 (350)
12 1/2 2 2,1 31 (310)
16 5/8 2,5 2,41 24 (240)
20 3/4 3 2,77 24 (240)
22 7/8 3 2,77 21 (210)
25 1 3 3,05 21 (210)
a
Maximum wall thickness that can be flared, due to connector design.
b
For working pressure applications higher than those given in this table, the manufacturer shall be consulted.
c 5 2 5
1 bar = 10 N/m = 10 Pa = 0,1 MPa.

TTabablele 1 1 ((ccoonnttiinnueuedd))
Maximum wall thickness of
b
Tube outside diameter (OD) Maximum working pressure
a
tube for flaring
Metric Inch Metric tube Inch tube Carbon steel and stainless steel
30 and 32 1 1/4 3 3,05 17 (170)
38 1 1/2 3 3,05 14 (140)
50 2 3,5 3,4 10,5 (105)
a
Maximum wall thickness that can be flared, due to connector design.
b
For working pressure applications higher than those given in this table, the manufacturer shall be consulted.
c 5 2 5
1 bar = 10 N/m = 10 Pa = 0,1 MPa.
6 Designation of connectors
6.1 Connectors shall be designated by an alphanumeric code to facilitate ordering. They shall be
designated by the word “Connector”, followed by ISO 8434-2, followed by a space, then the connector style
letter symbols (see 6.2), followed by a hyphen, then, for the ends, the outside diameter of the tube with
which they are to be connected, each separated by a multiplication symbol, ×. There shall be no space on
either side of the multiplication symbol. For stud ends (connector ends), the thread designation of the stud
end shall be added followed by a hyphen, and followed by connector material symbol.
6.2 The letter symbol designation of the connector style shall have three parts: a) the connection end type
immediately followed by b) the shape of the connector and c) by the indication that a complete connector is
being ordered. The letters A and B shall be used to distinguish different styles, where such options exist.
6.3 Tube ends are assumed to be external connections and thus do not need to be included in the
connection type code. However, if another type of connection is involved, it shall be designated.
6.4 Reducing connectors and elbows shall be designated by specifying the larger tube end first.
6.5 Stud connectors shall be designated by specifying the tube end first, then the thread size for the stud
end.
6.6 For tee connectors, the order of designation of the connection ends shall be from the larger to the
smaller tube end on the run, followed by the branch end.
6.7 For cross connectors, the order of designation of the connection ends shall be from left to right,
followed by from top to bottom, with the larger ends on the left and at the top.
6.8 The following letter symbols shall be used:
Connection end type Letter
Bulkhead BH
Swivel SW
Reducer RD
Stud SD
Shape Letter
Straight S
90° elbow E
45° elbow E45
Tee T
Run tee RT
Branch tee BT
Cross K
Long L
Component type Letter
Nut N
Sleeve SL
Locknut LN
Plug PL
Cap CP
Nipple NP
Metric M
Inch I
Completeness indication Letter
Complete connector C
Stud end sealing types Letter
Metal-to-metal sealing B
Elastomeric sealing E
O-ring sealing F
Material Letter
Steel S
Stainless steel SS
6.9 Examples of 37° flared connectors and designations are given in Figures 3 and 4.
EXAMPLE A straight stud connector (SDS), including O-ring without sleeve and nut, for use with 12 mm OD tubing
with an 3/4-16 UNF stud end in accordance with ISO 11926-3, made with steel, is designated for ordering as follows:
ConnectorISO 8434-2SDS-12×3/4-16F-S

Figure 3 — Straight stud connector (SDS) with stud end in accordance with ISO 11926-3
EXAMPLE A complete straight stud connector (SDSC), including O-ring with sleeve and nut, for use with 12 mm
OD tubing with an M16 × 1,5 stud end in accordance with ISO 6149-3, made with stainless steel, is designated for
ordering as follows:
ConnectorISO 8434-2SDSC-12×M16F-SS
Figure 4 — Straight stud connector, complete (SDSC) with stud end in accordance with ISO 6149-3
(sealing type F)
7 Requirements for tubes
7.1 The connectors shall be suitable for use with tubes with dimensions as given in Table 2 and Table 3.
The outside diameter tolerances include ovality. Tubes shall be free of scratches, damage, and imperfections
that would be considered detrimental to the function of the tubing.
7.2 Carbon steel tubes
7.2.1 Carbon steel tubes shall be seamless, cold drawn, and normalized. The steel tubes shall be weldable
and the content of carbon in its chemical composition shall not exceed 0,22 %.
7.2.2 Mechanical properties in normalized condition at room temperature shall be as follows.
Yield strength: R : 225 MPa
eh min.
Tensile strength: R : 340 to 630 MPa
m
Elongation after fracture: A : 25 % for R < 480 MPa
min. m
22 % for R 480 to 630 MPa
m
7.2.3 The following surface protections are recommended.
Tubes for welding purpose: phosphated or unplated.
Tubes for flaring purpose: zinc plated, passivated, phosphated, or unplated.
Plating applied should not exceed the tube outside diameter tolerance specified in Table 2 and Table 3 and
shall be compatible with the flaring process such that flare quality and cleanliness are not impacted.

7.2.4 Inspection and testing documentation shall be provided which contain at least the following
information:
— chemical analysis;
— tensile testing (see ISO 6892-1);
— tube forming drift expanding testing (see ISO 8493);
— dimensional inspection;
— non-destructive testing for the verification of hydraulic leaktightness (see ISO 10893-1);
— non-destructive testing for the detection of longitudinal imperfections (see ISO 10893-10);
— plating information.
7.3 Stainless steel tubes
7.3.1 Stainless steel tubes shall comply with ISO 1127.
7.3.2 Stainless steel tubes shall be cold-drawn, solution annealed, and scale-free. Tubes made of stainless
steel shall be suitable for welding.
7.3.3 Mechanical properties after heat treatment at room temperature shall be as follows:
Yield strength: R : 245 MPa
p0,2 min.
Tensile strength: R : 500 to 730 MPa
m
Elongation after fracture: A : 35 %
min.
Reference hardness: max. 90 HRB in accordance with ISO 6508-1
7.3.4 Inspection and testing documentation shall be provided which contain at least the following
information:
— chemical analysis;
— tensile testing (see ISO 6892-1);
— tube forming drift expanding testing (see ISO 8493) or Ring-expanding test (see ISO 8495);
— resistance to intergranular corrosion (see ISO 3651-2);
— dimensional inspection;
— non-destructive testing for the verification of hydraulic leaktightness (see ISO 10893-1);
— non-destructive testing for the detection of longitudinal imperfections (see ISO 10893-10).

Table 2 — Metric tube sizes
Tube OD Limits of OD
mm mm
min. max.
4 3,9 4,1
5 4,9 5,1
6 5,9 6,1
8 7,9 8,1
10 9,9 10,1
12 11,9 12,1
16 15,9 16,1
20 19,9 20,1
22 21,9 22,1
25 24,9 25,1
30 29,85 30,15
32 31,85 32,15
38 37,85 38,15
50 49,8 50,2
Metric tubing shall be preferred.
Table 3 — Inch tube sizes
Tube OD Limits of OD
mm
a
in mm
min. max.
1/8 3,18 3,08 3,28
3/16 4,76 4,66 4,86
1/4 6,35 6,25 6,45
5/16 7,94 7,84 8,04
3/8 9,52 9,42 9,62
1/2 12,7 12,6 12,8
5/8 15,88 15,78 15,98
3/4 19,05 18,95 19,15
7/8 22,22 22,12 22,32
1 25,4 25,3 25,5
1 1/4 31,75 31,6 31,9
1 1/2 38,1 37,95 38,25
2 50,8 50,6 51
a
Equivalent dimension in millimetres.
8 Across flats dimensions and tolerances
8.1 The dimensions across flats of elbow, tee and cross connectors shall be as shown in the respective
tables with minus tolerance only. For sizes up to and including 24 mm, tolerances for across flats dimensions
0 0
for forgings shall be mm, and for sizes larger than 24 mm, they shall be mm. The basic forging size
−0,8 −1,0
may be increased up to the maximum size shown for barstock, but the size selected shall be a metric
across-flat size with minus tolerance only.

8.2 Hex tolerances shall be in accordance with ISO 4759-1, product grade C. Minimum across corner hex
dimensions are 1,092 times the nominal width across flats. The minimum side flat is 0,43 times the nominal
width across flats, unless otherwise specified or shown, hex corners shall be chamfered 15° to 30° to a
diameter equal to the width across flats, with a tolerance of mm.
−0,4
9 Design
9.1 Connectors
The connectors shall conform to the requirements given in Figures 5 to 19 and Tables 6 to 20. They shall be
designed so that resistance to flow is reduced to a minimum.
9.2 Dimensions
Dimensions specified apply to finished parts, including any plating or other treatments. The tolerance
value for all dimensions not otherwise limited shall be ±0,4 mm. The sealing seats of connectors shall be
concentric, with straight thread pitch diameters within 0,25 mm full indicator reading (FIR).
9.3 Passage tolerances
Where passages in straight connectors are machined from opposite ends, the offset at the meeting point
shall not exceed 0,4 mm. No cross-sectional area at a junction of passages shall be less than that of the
smallest passage.
9.4 Wall thickness
Unless otherwise designated, the wall thickness at any point on the connectors shall not be less than the
thickness established by the specified dimensions, tolerances, and eccentricities for inner and outer surfaces.
9.5 Angular tolerances
Angular tolerance on axes of end on elbows, tees, and crosses shall be ±2,5° for tube sizes up to and including
10 mm and ±1,5° for all larger sizes.
9.6 Contour details
Details of contour shall be chosen by the manufacturer, provided the dimensions given in Tables 6 to 20 are
maintained. Wrench flats on elbows, tees, and crosses shall conform to the dimensions given in the relevant
tables. Abrupt reduction of a section shall be avoided. Junctions of small external sections and adjoining
sections that are relatively heavy shall be blended by means of ample fillets.
9.7 Stud ends
The dimensions for the stud ends shall conform to those given in ISO 6149-3. Stud ends in accordance with
ISO 1179-3, ISO 9974-2 and ISO 11926-3 shall not be used for new designs in fluid power applications.
9.8 Reducing connectors
Dimension of reducing connectors shall be in accordance with Annex A.

10 Screw threads
10.1 37° flared ends
The screw threads on the tube flared ends of the connectors shall be ISO inch screw threads in accordance
with ISO 725. Straight threads shall be class 2A or 2B, except external threads which are plated or coated
may exceed 2A diameters but shall not exceed maximum of 3A diameters. Internal threads of all classes
shall be within specified limits after plating or coating.
When external threads are produced by thread rolling and the body is not undercut, the unthreaded area
adjacent to the shoulder may be reduced to the minimum pitch diameter.
External threads shall be chamfered and internal threads shall be countersunk as specified.
10.2 Stud ends (connection ends)
The screw threads for stud ends of connectors shall be in accordance with the applicable defined stud end
standard. The dimensions of the stud end connectors shall comply with the requirements given in this
document.
11 Manufacture
11.1 Construction
Unless otherwise specified, connectors shall be made from carbon steel.
Stainless steel connectors shall be made from the material specified by the user and shall be passivated.
Carbon steel and stainless steel connectors fabricated from multiple components must be bonded together
with materials having a melting point of not less than 1 000 °C (1 832 °F).
11.2 Workmanship
Workmanship shall conform to the best commercial practice to produce high-quality connectors. Connectors
shall be free from visual contaminants, all hanging burrs, loose scale and slivers which might be dislodged
in use and any other defects that might affect the function of the parts. All machined surfaces shall have
a surface roughness value of MRR Ramax 6,3 specified in accordance with ISO 21920-1, except where
otherwise specified.
11.3 Corrosion protection
The external surfaces and threads of all carbon steel parts shall be plated or coated with a suitable material
that passes a salt spray test in accordance with ISO 9227. The following requirements shall apply:
a) No appearance of corrosion products of the protective coating before 96 h.
b) No appearance of corrosion products of the base metal before 144 h.
The following exceptions shall apply:
a) All internal fluid passages.
b) Edges such as hex points, serrations and crests of threads where there may be mechanical deformation
of the plating or coating typical of mass-produced parts or shipping effects.
c) Areas where there is mechanical deformation of the plating or coating caused by crimping, flaring
bending and other post-plate metal forming operations.
d) Areas where the parts are suspended or affixed in the test chamber where condensate can accumulate.

Parts manufactured to this specification shall not be cadmium plated and shall not use hexavalent chromate
coatings. Internal fluid passages shall be protected from corrosion during storage and shipping. Changes in
plating or coating shall be re-qualified to ensure assembly torque is not affected.
11.4 Connector protection
By a method agreed between manufacturer and user, the face of the connectors and threads (both internal
and external) shall be protected by the manufacturer from nicks and scratches that would be detrimental
to the function of the connector. Passages shall be securely covered to prevent the entrance of dirt or other
contaminants. Nuts and sleeves that are furnished separately from the connector shall be protected from
rust, but do not require capping.
11.5 Corners
Unless otherwise noted, all sharp corners shall be broken to 0,15 mm maximum.
12 Assembly instructions
The assembly of the connectors with the connecting tubes shall be carried out without external loads.
Upon request the manufacturer shall provide assembly instructions for the use of the connectors. These
instructions should include the following information:
— details relating to material and quality of suitable tubes;
— details concerning the preparation of the selected tube;
— instructions regarding the assembly of the connector, such as number of wrenching turns or assembly
torque;
— recommendations regarding the tools to be used for assembly;
— torque values listed in Table 5 are for controlled testing to establish compliance to the performance
requirements set forth in Table 4. Recommended assembly torques by manufacturers may vary from
Table 5;
— smaller sizes (–2 through –8) of 37° flare connectors are less tolerant to overtightening than the larger
sizes. Overtightening in these sizes causes deformation of 37° cone of the male end. Excessive deformation
of the cone results in loss of clamping force and, hence, loss of seal. It can also reduce flow area.
13 Procurement information
The following information should be supplied by the user when making an inquiry or placing an order. Refer
to the designation of connectors in in Clause 6 for additional information:
— description of connector;
— material of connector;
— material and size of tube;
— fluid to be conveyed;
— working pressure;
— fluid working temperature range;
— ambient temperature range;
— seal material.
14 Marking of components
Connector bodies and nuts shall be permanently marked with the manufacturer's name, trademark or code
identifier, unless otherwise agreed upon by the user and manufacturer. Nuts to be used with connectors
used with 30 mm and 32 mm tubes shall be marked with the relevant tube outside diameter.
15 Performance and qualification test
15.1 Performance requirements
The following outlines the performance test requirements for standard 37° flared connectors. Connectors,
swivel nuts, and sleeves shall be tested in accordance with ISO 19879, unless otherwise specified. In addition
to the test requirements and procedures specified, all components must be able to pass the performance
requirements in the as-shipped condition (e.g. annealed components, plating, coatings, rust preventative).
Working pressures for connectors, tube connections, cap nuts, and hose fittings shall be as listed in Table 4
or as specified in respective clause. Proof pressures shall be twice the working pressures and minimum
burst pressures shall be four times the working pressures.
15.1.1 Proof test
For each size, nine test assemblies in accordance with ISO 19879 shall be subjected to the proof test procedure
specified in ISO 19879, prior to burst and cyclic endurance tests. They shall not leak at the respective proof
pressures given in Table 4.
Table 4 — Test pressures for steel and stainless steel 37° flared connections
Maximum work-
Tube OD Test pressures
a
ing pressure
Metric Inch Proof Burst Cyclic endurance
b
Mm in MPa (bar) MPa (bar) MPa (bar) MPa (bar)
4 1/8 35 (350) 70 (700) 140 (1 400) 46,6 (466)
5 3/16 35 (350) 70 (700) 140 (1 400) 46,6 (466)
6 1/4 35 (350) 70 (700) 140 (1 400) 46,6 (466)
8 5/16 35 (350) 70 (700) 140 (1 400) 46,6 (466)
10 3/8 35 (350) 70 (700) 140 (1 400) 46,6 (466)
12 ½ 31 (310) 62 (620) 124 (1 240) 41,2 (412)
16 5/8 24 (240) 48 (480) 96 (960) 31,9 (319)
20 ¾ 24 (240) 48 (480) 96 (960) 31,9 (319)
22 7/8 21 (210) 42 (420) 84 (840) 27,9 (279)
25 1 21
...

ISO/TC 131/SC 04 4
Secretariat: ANSI
Date: 2026-06-30xx
Metallic tube connections for fluid power and general use —
Part 2:
37° Flared degree flared connectors
Raccordements de tubes métalliques pour transmissions hydrauliques et pneumatiques et applications
générales —
Partie 2: Connecteurs évasés à 37 degrés
FDIS stage
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Materials . 3
4.1 General . 3
4.2 Connector bodies . 4
4.3 Nuts . 4
4.4 Sleeves . 4
5 Pressure and temperature requirements . 4
6 Designation of connectors . 5
7 Requirements for tubes . 7
8 Across flats dimensions and tolerances . 10
9 Design . 10
9.1 Connectors . 10
9.2 Dimensions . 10
9.3 Passage tolerances . 10
9.4 Wall thickness . 10
9.5 Angular tolerances . 10
9.6 Contour details . 10
9.7 Stud ends . 11
9.8 Reducing connectors . 11
10 Screw threads . 11
10.1 37° flared ends . 11
10.2 Stud ends (connection ends) . 11
11 Manufacture . 11
11.1 Construction . 11
11.2 Workmanship . 11
11.3 Corrosion protection . 11
11.4 Connector protection. 12
11.5 Corners . 12
12 Assembly instructions . 12
13 Procurement information . 13
14 Marking of components . 13
15 Performance and qualification test . 13
15.1 Performance requirements . 13
16 Identification statement . 15
Annex A (normative) Length reduction factors for reducing connectors . 51
Bibliography . 61

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee SC 4,
Connectors and similar products and components.
This third edition cancels and replaces the second edition (ISO 8434-2:2007), which has been technically
revised.
The main changes are as follows:
— — Introduction and Clause 10Clause 10,, ISO 263 cross-references replaced with ISO 725.
— Clause 1— Clause 1 “Scope” updated to include tubes with outside diameters from 4 mm to 50,8 mm. Sizes
4, 5, and 22 mm have been added to all applicable tables.
— Clause 2— Clause 2 “Normative references” updated.
— Clause 3— Clause 3 “Terms and definitions” updated. Figure 1Figure 1 added.
— 4.2— 4.2,, removed all references to connector bodies made from copper alloys.
— 5.3— 5.3,, removed pressure derating for connectors made from stainless steel.
— 6.7— 6.7,, added material and letter designations.
— Clause 7— Clause 7 “Requirements for tubes” rewritten to remove references to ISO 3304 and ISO 3305.
— 8.1— 8.1,, added forging size criteria.
iv
— 9.4— 9.4 “Wall Thickness” added.
— Clause 10— Clause 10 “Screw Threads” rewritten.
— 11.3— 11.3 “Corrosion protection” rewritten.
— Clause 12— Clause 12 “Assembly Instructions” rewritten.
— Clause 13— Clause 13 “Procurement information” seal material added.
— 15.1— 15.1 “Performance requirements” rewritten.
— 15.1.5—
— — Clause 15.1.5 “Repeated assembly test” added, “Re-use of test samples” removed.
— Clause 16— Clause 16 “Identification statement” rewritten.
— — All figures have been renumbered and redrawn.
— Figure 5— Figure 5,, tolerance added to R0,5 radius.
— Figure 7— Figure 7 and Table 8Table 8 were added for the recommended chamfer for single flares.
a
— Table 9— Table 9,, footnote “ ” added.
— Figure 10— Figure 10,, R0,26 ± 0,13 changed to R0,25 ± 0,15.
— Figure 11/Table 12— Figure 11/Table 12,, added “L ” dimension and subsequent “L” dimensions
were adjusted in following figures and tables.
— Table 13— Table 13,, removed Tube OD 50.
— Figure 18— Figure 18/Table 19/Table 19 and Figure 19/Table 20Figure 19/Table 20,,
Optional dual angle seat design added.
— Figure 19— Figure 19/Table 20/Table 20 added “L ”.
— Table A.3— Table A.3 factor for 9/16-18 and 16 updated to -0,4.
— — Bibliography updated.
A list of all parts in the ISO 8434 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
v
Introduction
In fluid power systems, power is transmitted and controlled through a fluid (liquid or gas) under pressure
within an enclosed circuit. In general applications, a fluid may be conveyed under pressure.
Components may be connected through their ports by connections (connectors), tubes and hoses. Tubes are
rigid conductors; hoses are flexible conductors.
[1][1] [2] [3]
This document is based on the US standard ANSI/SAE J514-1 and SAE J533 . . The threads for the 37°
flared connection are unified inch threads in accordance with ISO 725. The inch threads were not changed to
metric threads according to ISO 261 to allow connectors complying with this document to be used in existing
applications without requiring a change to tube or hose assemblies. Also, the thread-to-nut overtightening and
seal performance have been extensively tested; to change to metric threads would require an extensive test
program at considerable cost without providing any functional improvement. The threads are integral to
themselves, connectors of this type match only to themselves and, other than having metric threads, no value
in changing could be found. Major international companies that have used these connectors have adopted the
design without noting any problems. All wrench flats specified in this document are dimensioned to be used
with ISO standard metric wrenches.
vi
Metallic tube connections for fluid power and general use — Part 2:
37° flared connectors
Part 2:
37 degree flared connectors
1 Scope
This document specifies the general and dimensional requirements for the design and performance of
37° flared connectors that are suitable for use with ferrous and non-ferrous tubes with outside diameters from
4 mm to 50,8 mm, inclusive. These connectors provide full-flow connections with metal-to-metal sealings.
These connectors are for use in fluid power and general applications within the limits of pressure and
temperature specified in this document.
They are intended for the connection of tubes and hose fittings to ports in accordance with ISO 6149--1,
ISO 1179--1, ISO 9974--1 and ISO 11926--1. (See ISO 12151--5 for related hose fitting specification.)
NOTE 1 For new designs in hydraulic fluid power applications, see the requirements given in 9.79.7. Where the
requirements of the application allow for the use of elastomeric seals, connector designs that conform to International
Standards and incorporate elastomeric sealing are preferred.
NOTE 2 For use under conditions outside the limits for pressure or temperature, or both, see 5.45.4.
Both metric and inch tubing can be accommodated by changing the sleeve (see Figure 9Figure 9).). In the past,
these connectors have been used predominantly with inch tubing. For new and future designs, the use of
metric tubing is preferred.
This document also specifies performance and qualification tests for 37° flared connectors.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 725, ISO inch screw threads — Basic dimensions
ISO 1127, Stainless steel tubes — Dimensions, tolerances and conventional masses per unit length
ISO 1179--3, Connections for general use and fluid power — Ports and stud ends with ISO 228-1 threads with
elastomeric or metal-to-metal sealing — Part 3: Light-duty (L series) stud ends with sealing by O-ring with
retaining ring (types G and H))
ISO 4759--1, Tolerances for fasteners — Part 1: Bolts, screws, studs and nuts — Product grades A, B and C
ISO 5598, Fluid power systems and components — Vocabulary
ISO 6149--3, Connections for hydraulic fluid power and general use — Ports and stud ends with ISO 261 metric
threads and O-ring sealing — Part 3: Dimensions, design, test methods and requirements for light-duty (L series)
stud ends
ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests
ISO 9974--2, Connections for general use and fluid power — Ports and stud ends with ISO 261 threads with
elastomeric or metal-to-metal sealing — Part 2: Stud ends with elastomeric sealing (type E))
ISO 11926--3, Connections for general use and fluid power — Ports and stud ends with ISO 725 threads and O-
ring sealing — Part 3: Light-duty (L series) stud ends
ISO 19879, Metallic tube connections for fluid power and general use — Test methods for hydraulic fluid power
connections
ISO 21920-1, Geometrical product specifications (GPS) — Surface texture: Profile — Part 1: Indication of surface
texture
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5598 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
3.1 3.1
adjustable stud end
stud end connector that allows for connector orientation through final tightening of the locknut to complete
the connection
Note 1 to entry: This type of stud end is typically used on shaped connectors (e.g. tees, crosses and elbows).
3.2 3.2
non-adjustable stud end
stud end connector that does not require specific orientation before final tightening of the connection because
it is only used on straight connectors
3.3 3.3
run
two principal, axially aligned outlets of a tee connector or cross connector
8434-2_ed3fig1.EPS
Key
1 run
2 branch
Figure 1 — Run and branch illustration
3.4 3.4
branch
side outlet(s) of a tee connector or cross connector
3.5 3.5
chamfer
removal of a conical portion at the entrance of a thread to assist assembly and prevent damage to the start of
the thread
3.6 3.6
assembly torque
torque required to achieve a satisfactory final connection
3.7 3.7
qualification test torque
torque used to verify conformity of the connector to the requirements of this document
3.8 3.8
overtightening
torque that the nut withstands without deformation that renders it unusable
3.9 3.9
jump size connector
connectorsconnector with dis-similar end connections, for example, -–6 male flare with a -–12 stud end
4 Materials
4.1 General
Figure 2Figure 2 shows the cross-section and components of a typical 37° flared connector.
8434-2_ed3fig2.EPS
Key
1 straight stud connector body
2 tube nut
3 tube
4 sleeve
5 O-ring
a
Stud end in accordance with ISO 1179-3, ISO 6149-3, ISO 9974-2 or ISO 11926-3.
Figure 2 — Cross-section of typical 37° flared connection
4.2 Connector bodies
Bodies shall be manufactured from carbon steel or stainless steel, which will provide the minimum
requirements for the pressure and temperature ratings specified in Clause 5Clause 5 when tested in
accordance with Clause 15Clause 15. They shall have characteristics that make them suitable for use with the
fluid to be conveyed and to provide an effective joint.
4.3 Nuts
Nuts to be used with carbon steel bodies shall be made of carbon steel and those for use with stainless steel
bodies shall be made of stainless steel unless otherwise specified.
4.4 Sleeves
Sleeves shall be manufactured from a material similar to the bodies.
5 Pressure and temperature requirements
5.1 5.1 The working pressure of the connector shall be the lower of the working pressure of the
37° flared connector connection given in Table 1Table 1 and the working pressure of the respective stud
end.
5.2 5.2 Flared connectors in accordance with this document made of carbon steel shall meet or exceed
without leakage the requirements to the working pressures given in Table 1Table 1 when used at
temperatures from −40 °C to +120 °C with petroleum base hydraulic fluids.
5.3 5.3 Connectors made of stainless steel complying with this document shall be suitable for use at
the working pressures given in Table 1Table 1 when used at temperatures from −60 °C to +50 °C.
5.4 5.4 For applications under conditions outside the limits for pressure or temperature, or both given
in Table 1Table 1 and in 5.25.2 and 5.35.3,, the manufacturer shall be consulted.
5.5 5.5 Connectors conforming to this document shall be tested in accordance with
Clause 15Clause 15 to ensure that they meet or exceed the pressure requirements given in
Table 1Table 1.
5.6 5.6 The pressure and temperature requirements given in Table 1Table 1 and in 5.25.2 and
5.35.3 are for tube connections and connector bodies only. For port and stud end pressure and temperature
ratings, the values in the respective port and stud end standards shall apply.
5.7 5.7 To achieve these maximum working pressures with a 4:1 design factor, the maximum tube wall
thicknesses shown in Table 1Table 1 are sufficient. See ISO 10763 to confirm the necessary tube wall
thickness for a specific working pressure.
Table 1 — Working pressures for 37° flared connections
Tube outside diameter Maximum wall thickness of Maximum working
a b
(OD) tube for flaring pressure
Carbon steel and stainless
Metric Inch Metric tube Inch tube
steel
c
mm in mm mm MPa (bar)
4 1/8 1 0,89 35 (350)
5 3/16 1 0,89 35 (350)
6 1/4 1,5 1,65 35 (350)
Tube outside diameter Maximum wall thickness of Maximum working
a b
(OD) tube for flaring pressure
Carbon steel and stainless
Metric Inch Metric tube Inch tube
steel
8 5/16 1,5 1,65 35 (350)
10 3/8 1,5 1,65 35 (350)
12 1/2 2 2,1 31 (310)
16 5/8 2,5 2,41 24 (240)
20 3/4 3 2,77 24 (240)
22 7/8 3 2,77 21 (210)
25 1 3 3,05 21 (210)
30 and 32 1 1/4 3 3,05 17 (170)
38 1 1/2 3 3,05 14 (140)
50 2 3,5 3,4 10,5 (105)
a Maximum wall thickness that can be flared, due to connector design.
b For working pressure applications higher than those given in this table, the manufacturer shall be consulted.
5 2 5
c 1 bar = 10 N/m = 10 Pa = 0,1 MPa.
6 Designation of connectors
6.1 6.1 Connectors shall be designated by an alphanumeric code to facilitate ordering. They shall be
designated by the word “Connector”, followed by ISO 8434-2, followed by a space, then the connector style
letter symbols (see 6.26.2),), followed by a hyphen, then, for the ends, the outside diameter of the tube with
which they are to be connected, each separated by a multiplication symbol, ×. There shall be no space on either
side of the multiplication symbol. For stud ends (connector ends), the thread designation of the stud end shall
be added followed by a hyphen, and followed by connector material symbol.
6.2 6.2 The letter symbol designation of the connector style shall have three parts: a) the connection
end type immediately followed by b) the shape of the connector and c) by the indication that a complete
connector is being ordered. The letters A and B shall be used to distinguish different styles, where such options
exist.
6.3 6.3 Tube ends are assumed to be external connections and thus do not need to be included in the
connection type code. However, if another type of connection is involved, it shall be designated.
6.4 6.4 Reducing connectors and elbows shall be designated by specifying the larger tube end first.
6.5 6.5 Stud connectors shall be designated by specifying the tube end first, then the thread size for
the stud end.
6.6 6.6 For tee connectors, the order of designation of the connection ends shall be from the larger to
the smaller tube end on the run, followed by the branch end.
6.7 6.7 For cross connectors, the order of designation of the connection ends shall be from left to right,
followed by from top to bottom, with the larger ends on the left and at the top.
6.8 6.8 The following letter symbols shall be used:
Connection end type Letter
Bulkhead BH
Swivel SW
Reducer RD
Stud SD
Shape Letter
Straight S
90° elbow E
45° elbow E45
Tee T
Run tee RT
Branch tee BT
Cross K
Long L
Component type Letter
Nut N
Sleeve SL
Locknut LN
Plug PL
Cap CP
Nipple NP
Metric M
Inch I
Completeness indication Letter
Complete connector C
Stud end sealing types Letter
Metal-to-metal sealing B
Elastomeric sealing E
O-ring sealing F
Material Letter
Steel S
Stainless steel SS
6.9 6.9 Examples of 37° flared connectors and designations are given in Figures 3Figures 3 and 44.
EXAMPLE A straight stud connector (SDS), including O-ring without sleeve and nut, for use with 12 mm OD tubing
with an 3/4-16 UNF stud end in accordance with ISO 11926-3, made with steel, is designated for ordering as follows:
Connector ISOConnectorISO 8434-2 SDS2SDS-12×3/4-16F-S
8434-2_ed3fig3.EPS
Figure 3 — Straight stud connector (SDS) with stud end in accordance with ISO 11926-3
EXAMPLE A complete straight stud connector (SDSC), including O-ring with sleeve and nut, for use with 12 mm OD
tubing with an M16 × 1,5 stud end in accordance with ISO 6149-3, made with stainless steel, is designated for ordering
as follows:
Connector ISOConnectorISO 8434-2 SDSC2SDSC-12×M16F-SS
8434-2_ed3fig4.EPS
Figure 4 — Straight stud connector, complete (SDSC) with stud end in accordance with ISO 6149-3
(sealing type F)
7 Requirements for tubes
7.1 7.1 The connectors shall be suitable for use with tubes with dimensions as given in
Table 2Table 2 and Table 3Table 3. The outside diameter tolerances include ovality. Tubes shall be free
of scratches, damage, and imperfections that would be considered detrimental to the function of the tubing.
7.2 7.2 Carbon steel tubes
7.2.1 7.2.1 Carbon steel tubes shall be seamless, cold drawn, and normalized. The steel tubes shall be
weldable and the content of carbon in its chemical composition shall not exceed 0,22 %.
7.2.2 7.2.2 Mechanical properties in normalized condition at room temperature shall be as follows.
Yield strength: R : 225 MPa
eh min.
Tensile strength: R : 340 to 630 MPa
m
Elongation after fracture: A : 25 % for R < 480 MPa
min. m
22 % for R 480 to 630 MPa
m
7.2.3 7.2.3 The following surface protections are recommended.
Tubes for welding purpose: phosphated or unplated.
Tubes for flaring purpose: zinc plated, passivated, phosphated, or unplated.
PlatingsPlating applied should not exceed the tube outside diameter tolerance specified in Table 2Table 2 and
Table 3Table 3 and shall be compatible with the flaring process such that flare quality and cleanliness are not
impacted.
7.2.4 7.2.4 Inspection and testing documentation shall be provided which contain at least the following
information:
— — chemical analysis;
— — tensile testing (see ISO 6892-1);
— — tube forming drift expanding testing (see ISO 8493);
— — dimensional inspection;
— — non-destructive testing for the verification of hydraulic leaktightness (see ISO 10893-1);
— — non-destructive testing for the detection of longitudinal imperfections (see ISO 10893-10);
— — plating information.
7.3 7.3 Stainless steel tubes
7.3.1 7.3.1 Stainless steel tubes shall comply with ISO 1127.
7.3.2 7.3.2 Stainless steel tubes shall be cold-drawn, solution annealed, and scale-free. Tubes made of
stainless steel shall be suitable for welding.
7.3.3 7.3.3 Mechanical properties after heat treatment at room temperature shall be as follows:
Yield strength: R : 245 MPa
p0,2 min.
Tensile strength: R : 500 to 730 MPa
m
Elongation after fracture: A : 35 %
min.
Reference hardness: max. 90 HRB in accordance with ISO 6508-1
7.3.4 7.3.4 Inspection and testing documentation shall be provided which contain at least the following
information:
— — chemical analysis;
— — tensile testing (see ISO 6892-1);
— — tube forming drift expanding testing (see ISO 8493) or Ring-expanding test (see ISO 8495);
— — resistance to intergranular corrosion (see ISO 3651-2);
— — dimensional inspection;
— — non-destructive testing for the verification of hydraulic leaktightness (see ISO 10893-1);
— — non-destructive testing for the detection of longitudinal imperfections (see ISO 10893-10).
Table 2 — Metric tube sizes
Tube OD Limits of OD
mm mm
min. max.
4 3,9 4,1
5 4,9 5,1
6 5,9 6,1
8 7,9 8,1
10 9,9 10,1
12 11,9 12,1
16 15,9 16,1
20 19,9 20,1
22 21,9 22,1
25 24,9 25,1
30 29,85 30,15
32 31,85 32,15
38 37,85 38,15
50 49,8 50,2
Metric tubing shall be preferred.
Table 3 — Inch tube sizes
Tube OD Limits of OD
mm
a
in mm
min. max.
1/8 3,18 3,08 3,28
3/16 4,76 4,66 4,86
1/4 6,35 6,25 6,45
5/16 7,94 7,84 8,04
3/8 9,52 9,42 9,62
1/2 12,7 12,6 12,8
5/8 15,88 15,78 15,98
3/4 19,05 18,95 19,15
7/8 22,22 22,12 22,32
1 25,4 25,3 25,5
1 1/4 31,75 31,6 31,9
1 1/2 38,1 37,95 38,25
2 50,8 50,6 51
Tube OD Limits of OD
mm
a
in mm
min. max.
a  Equivalent dimension in millimetres.
8 Across flats dimensions and tolerances
8.1 8.1 The dimensions across flats of elbow, tee and cross connectors shall be as shown in the
respective tables with minus tolerance only. For sizes up to and including 24 mm, tolerances for across flats
𝟎𝟎  𝟎𝟎
dimensions for forgings shall be  mm, and for sizes larger than 24 mm, they shall be  mm. The basic
−𝟎𝟎,𝟖𝟖 −𝟏𝟏,𝟎𝟎
forging size may be increased up to the maximum size shown for barstock, but the size selected shall be a
metric across--flat size with minus tolerance only.
8.2 8.2 Hex tolerances shall be in accordance with ISO 4759-1, product grade C. Minimum across
corner hex dimensions are 1,092 times the nominal width across flats. The minimum side flat is 0,43 times the
nominal width across flats, unless otherwise specified or shown, hex corners shall be chamfered 15° to 30° to
𝟎𝟎
a diameter equal to the width across flats, with a tolerance of  mm.
−𝟎𝟎,𝟒𝟒
9 Design
9.1 Connectors
The connectors shall conform to the requirements given in Figures 5Figures 5 to 1919 and Tables 6Tables 6
to 2020. They shall be designed so that resistance to flow is reduced to a minimum.
9.2 Dimensions
Dimensions specified apply to finished parts, including any plating or other treatments. The tolerance value
for all dimensions not otherwise limited shall be ±0,4 mm. The sealing seats of connectors shall be concentric,
with straight thread pitch diameters within 0,25 mm full indicator reading (FIR).
9.3 Passage tolerances
Where passages in straight connectors are machined from opposite ends, the offset at the meeting point shall
not exceed 0,4 mm. No cross-sectional area at a junction of passages shall be less than that of the smallest
passage.
9.4 Wall thickness
Unless otherwise designated, the wall thickness at any point on the connectors shall not be less than the
thickness established by the specified dimensions, tolerances, and eccentricities for inner and outer surfaces.
9.5 Angular tolerances
Angular tolerance on axes of end on elbows, tees, and crosses shall be ±2,5° for tube sizes up to and including
10 mm and ±1,5° for all larger sizes.
9.6 Contour details
Details of contour shall be chosen by the manufacturer, provided the dimensions given in Tables 6Tables 6 to
2020 are maintained. Wrench flats on elbows, tees, and crosses shall conform to the dimensions given in the
relevant tables. Abrupt reduction of a section shall be avoided. Junctions of small external sections and
adjoining sections that are relatively heavy shall be blended by means of ample fillets.
9.7 Stud ends
The dimensions for the stud ends shall conform to those given in ISO 6149-3. Stud ends in accordance with
ISO 1179--3, ISO 9974--2 and ISO 11926--3 shall not be used for new designs in fluid power applications.
9.8 Reducing connectors
Dimension of reducing connectors shall be in accordance with Annex AAnnex A.
10 Screw threads
10.1 37° flared ends
The screw threads on the tube flared ends of the connectors shall be ISO inch screw threads in accordance
with ISO 725. Straight threads shall be class 2A or 2B, except external threads which are plated or coated may
exceed 2A diameters but shall not exceed maximum of 3A diameters. Internal threads of all classes shall be
within specified limits after plating or coating.
When external threads are produced by thread rolling and the body is not undercut, the unthreaded area
adjacent to the shoulder may be reduced to the minimum pitch diameter.
External threads shall be chamfered and internal threads shall be countersunk as specified.
10.2 Stud ends (connection ends)
The screw threads for stud ends of connectors shall be in accordance with the applicable defined stud end
standard. The dimensions of the stud end connectors shall comply with the requirements given in this
document.
11 Manufacture
11.1 Construction
Unless otherwise specified, connectors shall be made from carbon steel.
Stainless steel connectors shall be made from the material specified by the user and shall be passivated.
Carbon steel and stainless steel connectors fabricated from multiple components must be bonded together
with materials having a melting point of not less than 1 000 °C (1 832 °F).
11.2 Workmanship
Workmanship shall conform to the best commercial practice to produce high-quality connectors. Connectors
shall be free from visual contaminants, all hanging burrs, loose scale and slivers which might be dislodged in
use and any other defects that might affect the function of the parts. All machined surfaces shall have a surface
roughness value of MRR Ramax 6,3 specified in accordance with ISO 1302 21920-1, except where otherwise
specified.
11.3 Corrosion protection
The external surfaces and threads of all carbon steel parts shall be plated or coated with a suitable material
that passes a salt spray test in accordance with ISO 9227. The following requirements shall apply:
a) a) No appearance of corrosion products of the protective coating before 96 h.
b) b) No appearance of corrosion products of the base metal before 144 h.
The following exceptions shall apply:
a) a) All internal fluid passages.
b) b) Edges such as hex points, serrations and crests of threads where there may be mechanical
deformation of the plating or coating typical of mass-produced parts or shipping effects.
c) c) Areas where there is mechanical deformation of the plating or coating caused by crimping,
flaring bending and other post-plate metal forming operations.
d) d) Areas where the parts are suspended or affixed in the test chamber where condensate can
accumulate.
Parts manufactured to this specification shall not be cadmium plated and shall not use hexavalent chromate
coatings. Internal fluid passages shall be protected from corrosion during storage and shipping. Changes in
plating or coating shall be re-qualified to ensure assembly torque is not affected.
11.4 Connector protection
By a method agreed between manufacturer and user, the face of the connectors and threads (both internal
and external) shall be protected by the manufacturer from nicks and scratches that would be detrimental to
the function of the connector. Passages shall be securely covered to prevent the entrance of dirt or other
contaminants. Nuts and sleeves that are furnished separately from the connector shall be protected from rust,
but do not require capping.
11.5 Corners
Unless otherwise noted, all sharp corners shall be broken to 0,15 mm maximum.
12 Assembly instructions
The assembly of the connectors with the connecting tubes shall be carried out without external loads. Upon
request the manufacturer shall provide assembly instructions for the use of the connectors. These instructions
should include the following information:
— — details relating to material and quality of suitable tubes;
— — details concerning the preparation of the selected tube;
— — instructions regarding the assembly of the connector, such as number of wrenching turns or assembly
torque;
— — recommendations regarding the tools to be used for assembly;
— — torque values listed in Table 5Table 5 are for controlled testing to establish compliance to the
performance requirements set forth in Table 4Table 4. Recommended assembly torques by
manufacturers may vary from Table 5Table 5;;
— — smaller sizes (–2 through –8) of 37° flare connectors are less tolerant to overtightening than the larger
sizes. Overtightening in these sizes causes deformation of 37° cone of the male end. Excessive deformation
of the cone results in loss of clamping force and, hence, loss of seal. It can also reduce flow area.
13 Procurement information
The following information should be supplied by the user when making an inquiry or placing an order. Refer
to the designation of connectors in in Clause 6Clause 6 for additional information:
— — description of connector;
— — material of connector;
— — material and size of tube;
— — fluid to be conveyed;
— — working pressure;
— — fluid working temperature range;
— — ambient temperature range;
— — seal material.
14 Marking of components
Connector bodies and nuts shall be permanently marked with the manufacturer's name, trademark or code
identifier, unless otherwise agreed upon by the user and manufacturer. Nuts to be used with connectors used
with 30 mm and 32 mm tubes shall be marked with the relevant tube outside diameter.
15 Performance and qualification test
15.1 Performance requirements
The following outlines the performance test requirements for standard 37° flared connectors. Connectors,
swivel nuts, and sleeves shall be tested in accordance with ISO 19879, unless otherwise specified. In addition
to the test requirements and procedures specified, all components must be able to pass the performance
requirements in the as-shipped condition (e.g. annealed components, plating, coatings, rust preventative).
Working pressures for connectors, tube connections, cap nuts, and hose fittings shall be as listed in
Table 4Table 4 or as specified in respective clause. Proof pressures shall be twice the working pressures and
minimum burst pressures shall be four times the working pressures.
15.1.1 Proof test
For each size, nine test assemblies in accordance with ISO 19879 shall be subjected to the proof test procedure
specified in ISO 19879, prior to burst and cyclic endurance tests. They shall not leak at the respective proof
pressures given in Table 4Table 4.
Table 4 — Test pressures for steel and stainless steel 37° flared connections
Maximum
Tube OD working Test pressures
a
pressure
Metric Inch   Proof Burst Cyclic endurance
b
Mm in MPa (bar) MPa (bar) MPa (bar) MPa (bar)
4 1/8 35 (350) 70 (700) 140 (1 400) 46,6 (466)
Maximum
Tube OD working Test pressures
a
pressure
Metric Inch   Proof Burst Cyclic endurance
b
Mm in MPa (bar) MPa (bar) MPa (bar) MPa (bar)
5 3/16 35 (350) 70 (700) 140 (1 400) 46,6 (466)
6 1/4 35 (350) 70 (700) 140 (1 400) 46,6 (466)
8 5/16 35 (350) 70 (700) 140 (1 400) 46,6 (466)
10 3/8 35 (350) 70 (700) 140 (1 400) 46,6 (466)
12 ½ 31 (310) 62 (620) 124 (1 240) 41,2 (412)
16 5/8 24 (240) 48 (480) 96 (960) 31,9 (319)
20 ¾ 24 (240) 48 (480) 96 (960) 31,9 (319)
22 7/8 21 (210) 42 (420) 84 (840) 27,9 (279)
25 1 21 (210) 42 (420) 84 (840) 27,9 (279)
30/32 1 1/4 17 (170) 34 (340) 68 (680) 22,6 (226)
38 1 1/2 14 (140) 28 (280) 56 (560) 18,6 (186)
50 2 10,5 (105) 21 (210) 42 (420) 14 (140)
a  For working pressure applications higher than those given in Table 1Table 1,, the manufacturer shall be
consulted.
5 2 5
b  1 bar = 10 N/m = 10 Pa = 0,1 MPa.
15.1.2 Burst test
Three of the test assemblies that had been subjected to the proof test in 15.1.115.1.1 shall be used for the burst
test. The test shall be conducted in accordance with the burst test procedure specified in ISO 19879 and at the
minimum torque values given in Table 5Table 5. The test assemblies shall meet or exceed the minimum
required burst pressures given in Table 4Table 4.
Table 5 — Qualification test torque requirements
Overtighteni
a
Torque ng
Tube OD Thread
Torque
N⋅m
N⋅m
Metric Inch
N⋅m N⋅m
Mm in
4 1/8 5/16-24 UNF 8- to 9 15
5 3/16 3/8-24 UNF 11- to 12 19
6 1/4 7/16-20 UNF 15- to 16 24
8 5/16 1/2-20 UNF 19- to 21 31
10 3/8 9/16-18 UNF 24- to 28 42
12 1/2 3/4-16 UNF 49- to 53 80
16 5/8 7/8-14 UNF 77- to 85 114
Overtighteni
a
ng
Torque
Tube OD Thread
Torque
N⋅m
N⋅m
Metric Inch
N⋅m N⋅m
Mm in
20 3/4 1 1/16-12 UN 107- to 119 160
22 7/8 1 3/16-12 UN 127- to 140 186
25 1 1 5/16-12 UN 147- to 154 214
30/32 1-1/4 1 5/8-12 UN 172- to 181 271
38 1-1/2 1 7/8-12 UN 215- to 226 339
50 2 2 1/2-12 UN 332- to 350 497
a  These torque values are for qualification testing only and may differ from the assembly
torques supplied by the manufacturer.
15.1.3 Cyclic endurance (impulse) test
The remaining six test assemblies that were subjected to the proof test in 15.1.115.1.1 shall be subjected to
the cyclic endurance test procedure as specified in ISO 19879. The test shall be conducted at the minimum
torque values given in Table 5Table 5. The test assemblies shall pass a cyclic endurance test for
1 000 000 cycles at the respective impulse pressures given in Table 4Table 4.
15.1.4 Overtightening test
For each connector size, three samples each of the tube nut (N) and sleeve (SL) and the 90° swivel elbow
(SWE) nut shall be subjected to the overtightening test as specified in ISO 19879. Connector swivel nuts and
sleeves shall be capable of withstanding the overtightening qualification test with no indication of failure when
torqued to the overtightening values given in Table 5Table 5.
15.1.5 Repeated assembly test
Repeated assembly test shall be conducted at the maximum torque shown in Table 5Table 5 and pressures
shown in Table 4Table 4. Samples shall be assembled and disassembled ten times. Proof test per 15.1.115.1.1
shall be conducted following the first and tenth assembly. The test shall be conducted as specified in ISO
19879. The leakage test per ISO 19879 test procedure is not required unless requested by the customer.
Definition of failure after repeated assembly testing:
a) a) Nut cannot be removed by hand after breakaway.
b) b) Nut cannot swivel freely
...