ISO 2974

• Abstract:

  ISO 2974:2018 specifies the dimensional requirements of end-connections for high-pressure fuel injection equipment components, used on diesel (compression-ignition) engines. ISO 2974:2018 is applicable to externally threaded 60° female cones (see Figures 1, 2, 5, and 6) and intended for use with high-pressure fuel injection pipe assemblies with tube outside diameters of: - up to and including 12 mm for integral female cones (see Table 1); and - up to and including 9 mm for fabricated female cones (see Table 2). Details of the pipe connection ends referenced in this document are shown in ISO 13296.

• Status: Not Published
• ICS: 43.060.40 - Fuel systems
• Technical Committee: ISO/TC 22/SC 34 - Propulsion, powertrain and powertrain fluids
• Drafting Committee: ISO/TC 22/SC 34/WG 2 - Injection equipment
• Current Stage: 6000 - International Standard under publication
• Start Date: 23-Sep-2026
• Completion Date: 26-Sep-2026

• Revises: ISO 2974:2018 - Diesel engines — 60° female cones for high-pressure fuel injection components
• Effective Date: 28-Oct-2023

Overview

ISO 2974 specifies the dimensional requirements for 60° concave cones used as end-connections in high-pressure fuel injection components for diesel engines. This standard supports reliable connection design for fuel injectors, common rails, distribution blocks, injection pumps, and high-pressure supply pumps used in compression-ignition engines.

The document is especially relevant for applications where fuel injection pressure is very high and where consistent geometry helps reduce the risk of leakage, assembly issues, and joint failure. It covers both integral concave cones and fabricated concave cones, making it a practical reference for manufacturers and system integrators working with diesel fuel injection pipe assemblies.

Key Topics

ISO 2974 focuses on the core design and conformity requirements for high-pressure fuel connection ends, including:

• Dimensional requirements for externally threaded 60° female cones
• Tolerance provisions for integral and fabricated cone designs
• Thread compatibility in accordance with ISO metric screw thread practice
• Surface texture guidance aligned with ISO 21920-1
• Material and heat treatment considerations for sealing performance
• Designation rules for identifying compliant concave cones

The standard applies to high-pressure fuel injection pipe assemblies with tube outside diameters of:

• Up to 12 mm for integral female cones
• Up to 9 mm for fabricated female cones

ISO 2974 also references ISO 13296 for related pipe connection end details, helping users align cone design with broader high-pressure fuel injection pipe assembly requirements.

Applications

ISO 2974 is widely relevant in the automotive and engine manufacturing sectors, particularly for:

• Diesel fuel injection systems
• Common rail fuel injection assemblies
• High-pressure pump connections
• Injector and rail end-connections
• Design and quality control of fuel pipe interfaces

This standard is valuable for engineers and suppliers who need standardized connection geometry to support tight sealing, repeated assembly, and robust performance under demanding operating conditions. It is also useful in product development, inspection, and conformity assessment for fuel system components.

Related Standards

ISO 2974 works alongside several important ISO documents that support diesel engine fuel system design:

• ISO 13296 - Diesel engines - High-pressure fuel injection pipe assemblies - General requirements and dimensions
• ISO 261 - ISO general purpose metric screw threads
• ISO 21920-1 - Surface texture indication
• ISO 3508 - Thread run-outs for fasteners
• ISO 7876-4 - Fuel injection equipment vocabulary for high-pressure pipes and end-connections
• ISO 7876-5 - Vocabulary for common rail fuel injection systems

For organizations involved in diesel engine components, high-pressure fuel injection, and automotive sealing interfaces, ISO 2974 provides a focused dimensional standard that supports interoperability, durability, and consistent production quality.

FINAL DRAFT
International
Standard
ISO/FDIS 2974
ISO/TC 22/SC 34
Diesel engines — 60° concave cones
Secretariat: JISC
for high-pressure fuel injection
Voting begins on:
components
2026-07-28
Moteurs diesels — Raccords finaux à cône concave de 60° pour
Voting terminates on:
lignes d'injection de carburants haute pression
2026-09-22
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
ISO/FDIS 2974:2026(en) © ISO 2026

FINAL DRAFT
ISO/FDIS 2974:2026(en)
International
Standard
ISO/FDIS 2974
ISO/TC 22/SC 34
Diesel engines — 60° concave cones
Secretariat: JISC
for high-pressure fuel injection
Voting begins on:
components
Moteurs diesels — Raccords finaux à cône concave de 60° pour
Voting terminates on:
lignes d'injection de carburants haute pression
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 2974:2026(en) © ISO 2026

ii
ISO/FDIS 2974:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Dimensions and tolerances . .2
4.2 Materials .2
5 Designation . 2
6 Figures and tables . 3
6.1 Integral 60° concave cone . .3
6.2 Fabricated 60° concave cone .6
Bibliography .10

iii
ISO/FDIS 2974:2026(en)
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 documents 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 the following URL:
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 022, Road vehicles, Subcommittee SC 34,
Propulsion, powertrain and powertrain fluids.
This tenth edition cancels and replaces the ninth edition (ISO 2974:2018), which has been technically
revised.
The main changes are as follows:
— Language inclusivity was improved;
— New thread option M16 × 1,0 in Table 1;
— Updated reference standard ISO 21920-1 for roughness indication.
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.

iv
ISO/FDIS 2974:2026(en)
Introduction
To comply with recent exhaust gas regulations and fuel consumption regulations for internal combustion
engines, the fuel injection pressure of automobile diesel engines is generally 2 000 bar or more. Engines of
2 700 bar are also being introduced to the market.
Since this fuel injection pressure is extremely high, the dimensions and specifications of the 60° concave
cones for high pressure fuel connections are serialised. This is to prevent fuel leaking from the joint or other
failures.
v
FINAL DRAFT International Standard ISO/FDIS 2974:2026(en)
Diesel engines — 60° concave cones for high-pressure fuel
injection components
1 Scope
This document specifies the dimensional requirements of end-connections for high-pressure fuel injection
equipment components that are fuel injectors, CR injectors, common rails, distribution blocks, injection
pumps, high-pressure supply pumps used on diesel (compression-ignition) engines.
It is applicable to externally threaded 60° concave cones (see Figures 1, 2, 5, and 6) and intended for use
with high-pressure fuel injection pipe assemblies with tube outside diameters of:
— up to and including 12 mm for integral concave cones (see Table 1); and
— up to and including 9 mm for fabricated concave cones (see Table 2).
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 261, ISO general purpose metric screw threads — General plan
ISO 21920-1, Geometrical product specifications (GPS) — Surface texture: Profile — Part 1: Indication of surface
texture
ISO 3508, Thread run-outs for fasteners with thread in accordance with ISO 261 and ISO 262
ISO 13296, Diesel engines — High-pressure fuel injection pipe assemblies — General requirements and
dimensions
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: ava
...

ISO/FDIS 2974
ISO/TC 22/SC 34
Secretariat: JISC
Diesel engines — 60° concave cones for high-pressure fuel injection
components
Moteurs diesels — Raccords finaux à cône concave de 60° pour lignes d'injection de carburants haute pression
FDIS stage
ISO/FDIS 2974:2026(en)
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
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO/FDIS 2974:2026(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Dimensions and tolerances . 2
4.2 Materials . 2
5 Designation . 2
6 Figures and tables . 3
6.1 Integral 60° concave cone . 3
6.2 Fabricated 60° concave cone . 8
Bibliography . 13

iii
ISO/FDIS 2974:2026(en)
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 documents 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 the following URL::
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 022, Road vehicles, Subcommittee SC 34,
Propulsion, powertrain and powertrain fluids.
This tenth edition cancels and replaces the ninth edition (ISO 2974:2018), which has been technically revised.
The main changes compared to the previous edition are as follows:
— — Language inclusivity was improved;
— — New thread option M16 × × 1.,0 in Table 1Table 1;;
— — Updated reference standard ISO 21920-1 for roughness indication.
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.
iv
ISO/FDIS 2974:2026(en)
Introduction
To comply with recent exhaust gas regulations and fuel consumption regulations for internal combustion
engines, the fuel injection pressure of automobile diesel engines is generally 2 000 bar or more. Engines of
2 700 bar are also being introduced to the market.
Since this fuel injection pressure is extremely high, the dimensions and specifications of the 60° concave cones
for high pressure fuel connections are serialised. This is to prevent fuel leaking from the joint or other failures.
v
Diesel engines — 60° concave cones for high-pressure fuel injection
components
1 Scope
This document specifies the dimensional requirements of end-connections for high-pressure fuel injection
equipment components, that are fuel injectors, CR injectors, common rails, distribution blocks, injection
pumps, high-pressure supply pumps used on diesel (compression-ignition) engines.
It is applicable to externally threaded 60° concave cones (see Figures 1, 2, 5, and 6) and intended for use with
high-pressure fuel injection pipe assemblies with tube outside diameters of:
— up to and including 12 mm for integral concave cones (see Table 1); and
— up to and including 9 mm for fabricated concave cones (see Table 2).
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 261, ISO general purpose metric screw threads — General plan
ISO 21920--1, Geometrical product specifications (GPS) — Surface texture: Profile — Part 1: Indication of
surface texture
ISO 3508, Thread run-outs for fasteners with thread in accordance with ISO 261 and ISO 262
ISO 13296, Diesel engines — High-pressure fuel injection pipe assemblies — General requirements and
dimensions
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
integral concave cone
concave cone where the sealing cone and the thread are connected in the same part
Note 1 to entry: See Figures 1 and 2.
3.2
fabricated concave cone
concave cone where the sealing cone and the thread are separate parts prior to joining, e.g. by welding
Note 1 to entry: See Figures 5 and 6.

ISO/FDIS 2974:2026(en)
3.3
reference diameter
S
baseline for dimensioning of the concave cone and the pipe end form
Note 1 to entry: S can be coincident with the intended nominal sealing interface between the concave cone and the pipe
end form, or not.
4 Requirements
4.1 Dimensions and tolerances
The 60° concave cone and its relationship to the external thread shall meet the requirements of Figure 1
(integral concave cones) or Figure 5 (fabricated concave cones). However, for integral concave cones,
variations at the smaller end of the concave cone as shown in Figure 3 are acceptable.
Dimensions and tolerances are given in Table 1 (integral concave cones) and Table 2 (fabricated concave
cones). Unspecified details are left to the manufacturer's choice.
With reference to dimension T in Figures 1, 2, 5, and 6, the external thread may be either with or without
undercut. However, it shall be possible to screw the GO-gauge for the thread up to the plane specified by
dimension T.
Figure 4 and Figure 7 show the assemblies with pipe end connections for the integral and fabricated concave
cone types, respectively.
4.2 Materials
The specification of material and heat treatmen
...