ISO 6622-1:2021

Internal combustion engines - Piston rings - Part 1: Rectangular rings made of cast iron

This document specifies the essential dimensional features of rectangular rings made of cast iron, Types R, B, BA and M, having diameters up to and including 200 mm, used in reciprocating internal combustion piston engines. It is also applicable to piston rings of compressors working under similar conditions.

Moteurs à combustion interne — Segments de piston — Partie 1: Segments rectangulaires en fonte moulée

General Information

• Status: Published
• Publication Date: 09-Aug-2021
• ICS: 27.020 - Internal combustion engines
• Technical Committee: ISO/TC 22/SC 34 - Propulsion, powertrain and powertrain fluids
• Drafting Committee: ISO/TC 22/SC 34/WG 4 - Piston rings
• Current Stage: 6060 - International Standard published
• Start Date: 10-Aug-2021
• Due Date: 26-Jan-2021
• Completion Date: 10-Aug-2021

Relations

• Revises: ISO 6622-1:2003 - Internal combustion engines - Piston rings - Part 1: Rectangular rings made of cast iron
• Effective Date: 04-Feb-2017

Overview

ISO 6622-1:2021 - Internal combustion engines - Piston rings - Part 1: Rectangular rings made of cast iron - specifies the essential dimensional features for rectangular cast‑iron piston rings (Types R, B, BA, and M) with nominal diameters up to and including 200 mm. The standard applies to reciprocating internal‑combustion engine pistons and to compressors operating under similar conditions. This third edition (2021) updates the 2003 edition with clarified figures, added taper option (M6) and editorial improvements.

Key topics and technical requirements

• Ring types and geometry: Defines straight‑faced (R), barrel‑faced (B), asymmetrical barrel‑faced (BA) and taper‑faced (M) ring shapes with reference figures and dimension tables.
• Dimensional tables and figures: Provides detailed tables for gauge widths, barrel/taper dimensions, radial wall thickness options and ring forces (see Tables 1–14 and Figures 1–13 in the document).
• Face coatings and inlays: Describes face coating types (uncoated, fully faced, semi‑inlaid, inlaid) and minimum plating/coating thickness requirements for peripheral faces.
• Twist and chamfer features: Specifies permissible twist values, positive/negative twist types (IF, IW, IFV, etc.), chamfer and edge dimensions and manufacturer discretion where standard twist is invoked.
• Designation conventions: Examples show how to designate rings by type, nominal diameter and width, material subclass (e.g., MC12, MC51), and coating (e.g., CR3, SC2F).
• Force factors and performance data: Includes force factor tables and specific ring force/dimension relationships for standard and thicker radial wall designs.
• Normative references: Uses terms and definitions from ISO 6621-1 and refers to ISO 6621-4 for general specifications.

Applications and who uses it

ISO 6622-1:2021 is intended for:

• Engine designers and OEMs specifying piston rings for reciprocating internal combustion engines.
• Piston‑ring manufacturers and foundries producing cast‑iron rectangular rings.
• Compressor manufacturers selecting compatible rings for compressor pistons.
• Quality, procurement and testing teams ensuring correct ring geometry, coatings and designation compliance.
• Aftermarket and remanufacturing suppliers matching replacement rings to original specifications.

Practical benefits include consistent interchangeability, predictable sealing/force behaviour, clearer coating and twist requirements and reduced design ambiguity.

Related Standards (if applicable)

• ISO 6621-1: Vocabulary for piston rings (normative reference)
• ISO 6621-4: General specifications for piston rings (normative reference)
• Other parts in the ISO 6622 series and related ISO 662x standards covering different ring materials and shapes.

For selection, designers should consult the dimensional tables and force factors in ISO 6622-1 and cross‑reference ISO 6621‑4 requirements before finalizing piston‑ring choice.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 6622-1
Third edition
2021-08
Internal combustion engines — Piston
rings —
Part 1:
Rectangular rings made of cast iron
Moteurs à combustion interne — Segments de piston —
Partie 1: Segments rectangulaires en fonte moulée
Reference number
©
ISO 2021
© ISO 2021
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Overview . 1
5 Ring types and designation examples . 1
5.1 Overview . 1
5.2 Type R — Straight faced rectangular ring . 1
5.2.1 General features. 1
5.2.2 Designation . 2
5.3 Type B — Barrel faced rectangular ring . 2
5.3.1 General features. 2
5.3.2 Designation . 3
5.4 Type BA — Asymmetrical barrel faced rectangular ring h ≥ 1,2 mm . 4
5.4.1 General features. 4
5.4.2 Designation . 5
5.5 Type M — Taper faced rectangular ring . 5
5.5.1 General features. 5
5.5.2 Designation . 6
6 Common features . 6
6.1 Face coating types . 6
6.2 Face shape types . 7
6.3 Piston ring twist features . 7
6.3.1 Taper faced rectangular ring with partly cylindrical machined (LM) or
lapped (LP) peripheral surface. 9
6.4 Chamfered edges . 9
6.5 Type R, B, BA and M rings (fully faced, semi-inlaid and inlaid) — Plating/coating
thickness .11
6.6 Type R, B, BA, and M rings — Nitrided case depth .12
7 Force factors .12
8 Dimensions .13
Bibliography .26
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/d irectives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www. iso. org/p atents).
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/f oreword. html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 34,
Propulsion, powertrain and powertrain fluids.
This third edition cancels and replaces the second edition (ISO 6622-1:2003), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— figures were updated for a better understanding;
— added M6 taper in Table 3;
— added h dimension in Table 5;
— editorial adaptations according to ISO directives.
A list of all parts in the ISO 6622 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/m embers. html.
iv © ISO 2021 – All rights reserved

Introduction
The ISO 6622 series is one of a number of series of International Standards dealing with piston rings for
[2],[3],[4] [5] [6],[7], [8]
reciprocating internal combustion engines. Others are ISO 6621, ISO 6623, ISO 6624
[9], [10] [11],[12] [13]
, ISO 6625, ISO 6626 and ISO 6627 .
The common features and dimensional tables presented in this document constitute a broad range of
variables and, in selecting a particular ring type, it is important for the designer to bear in mind the
conditions under which it will be required to operate.
[3]
It is also important that the designer refers to the specifications and requirements of ISO 6621-3 and
ISO 6621-4 before completing selection.
INTERNATIONAL STANDARD ISO 6622-1:2021(E)
Internal combustion engines — Piston rings —
Part 1:
Rectangular rings made of cast iron
1 Scope
This document specifies the essential dimensional features of rectangular rings made of cast iron,
Types R, B, BA and M, having diameters up to and including 200 mm, used in reciprocating internal
combustion piston engines. It is also applicable to piston rings of compressors working under similar
conditions.
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 6621-1, Internal combustion engines — Piston rings — Part 1: Vocabulary
ISO 6621-4, Internal combustion engines — Piston rings — Part 4: General specifications
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6621-1 apply.
ISO and IEC maintain terminological 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/
4 Overview
The rectangular ring types are specified in Tables 1 to 3 and Figures 1 to 4. Their common features and
the dimensions of those features are specified in Tables 4 to 10 and Figures 5 to 13. Tables 11 and 12
give the force factors for the different ring types, while Tables 13 and 14 give the dimensions and forces
of rectangular rings of radial wall thickness regular and thicker “D/22”, respectively.
5 Ring types and designation examples
5.1 Overview
The rectangular ring types are specified in Tables 1 to 3 and Figures 1 to 4.
5.2 Type R — Straight faced rectangular ring
5.2.1 General features
See Table 13 or 14 for dimensions and forces.
Key
1 reference plane
a
t = 0,005 × h .
Figure 1 — Type R
5.2.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6622-1, being a rectangular
ring made of cast iron, with a straight faced peripheral surface (R), of nominal diameter d = 90 mm (90), of
nominal ring width h = 2,5 mm (2,5), made of non-heat treated grey cast iron, subclass 12 (MC12), phosphated
on all sides (PO):
Piston ring ISO 6622-1 R 90 × 2,5 - MC12/PO
5.3 Type B — Barrel faced rectangular ring
5.3.1 General features
See Table 13 or 14 for dimensions and forces.
2 © ISO 2021 – All rights reserved

Key
1 reference plane
a
See Table 1.
Figure 2 — Type B
Table 1 — Gauge width (h ) and barrel dimensions for symmetrical barrel faced compression
rings
Dimensions in millimetres
a b c
h h h h tolerance h t , t h
1 25 26 26 27 2 3 8
1,2 0,30 0,60 ±0,20 0,90 0,002.0,012 0,60
1,5 0,35 0,75 ±0,25 1,15 0,80
1,75 0,35 0,85 ±0,30 1,35 1,00
0,003.0,015
2,0 0,40 1,00 ±0,30 1,60 1,20
2,5 0,45 1,25 ±0,40 2,05 1,60
3,0 0,50 1,50 ±0,50 2,50 2,00
0,005.0,020
3,5 0,55 1,75 ±0,50 2,95 2,40
4,0 0,60 2,00 ±0,60 3,40 2,80
0,005.0,023
4,5 0,65 2,25 ±0,60 3,85 3,20
a
h may be lowered for rings with reduced edge dimensions.
b
t and/or t can be changed as agreed between edge dimensions.
2 3
c
Gauge width (h ) only informative; may be used only if agreed between manufacturer and client.
5.3.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6622-1, being a rectangular
ring made of cast iron, with a barrel faced peripheral surface (B), of nominal diameter d = 90 mm (90), of nominal
width h = 2,5 mm (2,5), made of heat-treated martensitic spheroidal graphite cast iron, subclass 51 (MC51), with
a chromium plated coating on the peripheral surface, and of minimum thickness 0,15 mm (CR3):
Piston ring ISO 6622-1 - B 90 × 2,5 - MC51/CR3
5.4 Type BA — Asymmetrical barrel faced rectangular ring h ≥ 1,2 mm
5.4.1 General features
See Table 13 or 14 for dimensions and forces.
Key
1 reference plane
2 top side identification mark
Figure 3 — Type BA
Table 2 — Asymmetrical barrel dimensions
Dimensions in millimetres
a b b
h h h h tolerance h t t
1 25 26 26 27 2 3
c
0,20 0,35 0,80
1,2 ±0,15 0,005…0,016
0,28 0,43 0,90 0…0,005
1,5 0,35 0,50 ±0,15 1,15 0,007…0,022
1,75 0,35 0,55 1,35 0,008…0,025
±0,20 0…0,007
2,0 0,40 0,60 1,50 0,009…0,030
2,5 0,45 0,70 1,80 0,011…0,035
±0,25 0…0,008
3,0 0,55 0,80 2,10 0,012…0,038
3,5 0,60 0,90 2,40 0,012…0,040
±0,30 0…0,009
4,0 0,65 0,95 2,80 0,013. 0,045
4,5 0,70 1,05 ±0,35 3,20 0…0,010 0,015. 0,050
a
h may be lowered for rings with reduced edge dimensions.
b
t and/or t may be varied as agreed between manufacturer and client.
2 3
c
Recommended for bottom edge smaller than 0,2 mm.
4 © ISO 2021 – All rights reserved

5.4.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6622-1, being a rectangular
ring made of cast iron, with an asymmetrical barrel faced peripheral surface (BA), of nominal diameter
d = 90 mm (90), of nominal width h = 2,5 mm (2,5), made of heat-treated martensitic spheroidal graphite
1 1
cast iron subclass 51 (MC51), and having a chromium plated coating on the peripheral surface with a minimum
thickness of 0,15 mm (CR3):
Piston ring ISO 6622-1 BA 90 × 2,5 - MC51/CR3
5.5 Type M — Taper faced rectangular ring
5.5.1 General features
See Table 13 or 14 for dimensions and forces.
Key
1 reference plane
2 top side identification mark
Figure 4 — Type M
Table 3 — Taper
Dimensions in minutes
Uncoated rings with peripheral surface turned and chromium plated or spray coated rings with
a
peripheral surface ground and chromium plated rings with surface not ground
Code
b b, c
with IF or IW (top side) with IFU or IWU (bottom side)
Taper Tolerance
d
Taper Tolerance Taper Tolerance
+40
c
M1 10 10 — —
M2 30 30 — —
M3 60 60 60
+60
+50
M4 90 90 90
0 +60
M5 120 120 120
M6 180 180 180
a
For chromium plated rings with tapered peripheral surface not ground, the tolerance shall be increased by 10
+60 +70
(e.g. M3 = 60: for M rings or for M rings (negative twist type) with IF or IW and IFU or IWU).
0 0
b
IF and IW, and IFU and IWU, are explained in Figures 7 and 8.
c
M1 should not be used for rings of width <1,5 mm or for those with a partly cylindrical peripheral surface.
d
For M rings (negative twist type) M3, M4 and M5, the twist angle should not exceed 90 % of the minimum taper angle.
5.5.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6622-1, being a rectangular
ring made of cast iron, with a 10’ taper faced peripheral surface (M1), of diameter d = 90 mm (90), of nominal
width h = 2,5 mm (2,5), made of heat treated grey cast iron, subclass 23 (MC23) and having an inlaid spray
coating on the peripheral surface with a minimum thickness of 0,1 mm (SC2F):
Piston ring ISO 6622-1 M1 90 × 2,5 - MC23/SC2F
6 Common features
6.1 Face coating types
Figure 5 shows the types of piston ring face coatings.
6 © ISO 2021 – All rights reserved

a) uncoated b) fully faced c) semi inlaid d) inlaid
Figure 5 — Piston ring face types
6.2 Face shape types
Figure 6 shows the types of piston ring face shapes.
a) Type R b) Type B c) Type BA d) Type M
straight faced barrel faced asymmetrical barrel taper faced
faced
Figure 6 — Types piston ring face shapes
6.3 Piston ring twist features
When the standard twist of 0,01/0,05 mm for rings ≤2 mm axial width and 0,01/0,04 mm for
rings >2 mm axial width per 2 mm of radial ring thickness is specified, the dimension a , the angle φ
x
and the width of the bevel are at the discretion of the manufacturer. In such cases, the design should
correspond to one or the other of the designs shown in Figures 7 and 8.
Figure 7 shows the types of piston ring positive twist features.
Dimensions in millimetres
a) Type IF b) Type IFV c) Type IW
internal bevel top side variable internal bevel on the internal step top side
top side
Key
1 top side identification mark
Reference Tables 4 and 5 for dimensions.
Figure 7 — Types piston ring positive twist features
Figure 8 shows the types of piston ring negative twist features.
Dimensions in millimetres
a) Type IFU b) Type IFVU c) Type IWU
internal bevel bottom side variable internal bevel on the internal step bottom side
bottom side
Key
1 top side identification mark
Reference Tables 4 and 5 for dimensions.
a
See Table 3.
Figure 8 — Types piston ring negative twist features
Table 4 — a , h and h dimensions for rings h < 1,5 mm
3 18 19 1
Dimensions in millimetres
a
a h , h
3 18 19
d
Tolerance Tolerance
0 0
30 ≤ d < 60 0,85 × a 0,6 × h
1 1 1
−02, −02, 5
0 0
60 ≤ d ≤ 90 0,9 × a 0,6 × h
1 1 1
−03, −02, 5
a
Dimension may not apply for IF and IFU rings because h is specified for
this feature.
Table 5 — a , h and h dimensions for rings h ≥ 1,5 mm
3 18 19 1
Dimensions in millimetres
a
a h h
3 18, 19
d
Tolerance Tolerance
0 0
30 ≤ d < 80 0,8 × a 0,6 × h
1 1 1
−02, −02, 5
0 0
80 ≤ d < 100 0,8 × a 0,6 × h
1 1 1
−03, −02, 5
0 0
100 ≤ d < 150 0,8 × a 0,6 × h
1 1 1
−03, −03, 5
0 0
150 ≤ d ≤ 200 0,8 × a 0,6 × h
1 1 1
−04, −04, 5
a
Dimension may not apply for IF and IFU rings because h is speci-
fied for this feature.
8 © ISO 2021 – All rights reserved

6.3.1 Taper faced rectangular ring with partly cylindrical machined (LM) or lapped (LP)
peripheral surface
Figure 9 shows a partly cylindrical machined or lapped Type M ring and the axial dimensions of the
cylindrical part of the peripheral surface h are shown in Table 6.
Key
1 top side identification mark
Figure 9 — Partly cylindrical machined or lapped Type M rings
Table 6 — Axial dimensions of the cylindrical part of peripheral surface h
Dimensions in millimetres
a
h h h
1 24 24
max. max.
each side of gap up to 30°
1,2 0,4 0,8
1,5 0,5 1,0
1,75 0,6 1,2
2,0 0,7 1,4
2,5 0,8 1,6
3,0 1,0 2,0
3,5 1,2 2,3
4,0 1,3 2,6
4,5 1,5 3,0
a
Partly cylindrical peripheral surface shall be visible.
6.4 Chamfered edges
Outside chamfered edges (KA) are shown in Figure 10. Inside chamfered edges (KI) are shown in
Figure 11. KA and KI dimensions are shown in Table 7.
a) Chamfer with step for nominal b) Chamfer KA
KA ≥ 0,3
NOTE KA applies to uncoated rings only.
Figure 10 — Outside chamfered edges, KA
a) Chamfer with step for nominal b) Chamfer KI
KI ≥ 0,3
Figure 11 — Inside chamfered edges, KI
10 © ISO 2021 – All rights reserved

Table 7 — KA and KI dimensions
Dimensions in millimetres
d KA KI
30 ≤ d < 50 ≤0,2 ≤0,2
50 ≤ d < 125 0,3 ± 0,1 0,3 ± 0,15
125 ≤ d < 175 0,4 ± 0,1 0,4 ± 0,15
175 ≤ d ≤ 200 0,5 ± 0,1 0,6 ± 0,20
6.5 Type R, B, BA and M rings (fully faced, semi-inlaid and inlaid) — Plating/coating
thickness
Figure 12 — Plating/coating thickness
Table 8 — Plating/spray coating thickness
Dimensions in millimetres
Chromium plating Spray coating Thickness
code code min.
CRF — 0,005
CR1 SC1 0,050
CR2 SC2 0,100
a a
CR3 SC3 0,150
a a
CR4 SC4 0,200
a
Not recommended for rings h ≤ 1,2.
Table 9 — PVD coating thickness
Dimensions in millimetres
Code Peripheral surface
min.
PC001 0,001
PC003 0,003
PC006 0,006
PC010 0,010
PC020 0,020
PC030 0,030
a
PC040 0,040
a
Not applicable to diamond-like carbon (DLC) coatings.
6.6 Type R, B, BA, and M rings — Nitrided case depth
Figure 13 — Nitrided case depth
Table 10 — Nitrided case
...