ISO 6626-2:2024

International
Standard
ISO 6626-2
Third edition
Internal combustion engines —
2024-07
Piston rings —
Part 2:
Coil-spring-loaded oil control rings
of narrow width made of cast iron
Moteurs à combustion interne — Segments de piston —
Partie 2: Segments racleurs régulateurs d'huile étroits, en fonte,
mis en charge par ressort hélicoïdal
Reference number
© ISO 2024
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Overview . 1
5 Piston ring types and designation . 2
5.1 Types DFS-C, DFS-CNP, SSF, GSF, DSF, DSF-NG, and SSF-L — General features and
dimensions .2
5.2 Type DSF-C ─ Coil-spring loaded bevelled edge oil control ring, chromium plated and
profile ground .2
5.2.1 General features and dimensions .2
5.2.2 Designation of a Type DSF-C piston ring in accordance with ISO 6626-2 .3
5.3 Type DSF-CNP ─ Coil-spring loaded bevelled edge oil control ring, chromium plated
not profile ground .4
5.3.1 General features and dimensions .4
5.3.2 Designation of a Type DSF-CNP piston ring in accordance with ISO 6626-2 .4
5.4 Type SSF ─ Coil-spring loaded slotted oil control ring with rectangular groove .5
5.4.1 General features and dimensions .5
5.4.2 Designation of a Type SSF piston ring in accordance with ISO 6626-2 .5
5.5 Type GSF ─ Coil-spring loaded double bevelled oil control ring .5
5.5.1 General features and dimensions .5
5.5.2 Designation of a Type GSF piston ring in accordance with ISO 6626-2 .6
5.6 Type DSF ─ Coil-spring loaded bevelled edge oil control ring .6
5.6.1 General features and dimensions .6
5.6.2 Designation of a Type DSF piston ring in accordance with ISO 6626-2 .7
5.7 Type DSF-NG ─ Coil-spring loaded bevelled edge oil control ring (face geometry similar
to type DSF-C or type DSF-CNP) .7
5.7.1 General features and dimensions .7
5.7.2 Designation of a Type DSF-NG piston ring in accordance with ISO 6626-2 .8
5.8 Type SSF-L ─ Coil-spring loaded slotted oil control ring with rectangular groove at
periphery and V-shaped groove beneath .8
5.8.1 General features and dimensions .8
5.8.2 Designation of a Type SSF-L piston ring in accordance with ISO 6626-2 .9
6 Common features . 9
6.1 Oil drainage by slots or holes .9
6.1.1 Arrangement of slots .9
6.1.2 Slot length .11
6.1.3 Arrangement of holes .11
6.1.4 Diameter and number of holes .11
6.2 Plating thickness — DSF-C and DSF-CNP (coil-spring loaded bevelled edge oil control
ring, chromium plated) .11
6.3 Peripheral edges at gap of chromium plated oil control rings . 12
6.4 Spring groove, slot, and land offsets . 12
7 Coil springs .12
7.1 Types of coil spring . 12
7.2 Latch pin and location of small pitch in the coil spring .14
7.3 Coil spring excursion (extended gap) .14
7.4 Position of coil spring gap and fixing . 15
7.5 Material . 15
8 Tangential force and nominal contact pressure .15
8.1 Tangential force, F . 15
t
iii
8.1.1 Force factors . 15
8.1.2 General tangential force, F . 15
t
8.1.3 Actual tangential force, F , and tolerance .16
t
8.1.4 Normalized tangential force, F .16
N
8.2 Nominal contact pressure, p .16
9 Dimensions .16
Bibliography .31

iv
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 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 22, Road vehicles, Subcommittee SC 34,
Propulsion, powertrain and powertrain fluids.
This third edition cancels and replaces the second edition (ISO 6626-2:2013), which has been technically
revised.
The main changes are as follows:
— classes of nominal contact pressure moved to ISO 6626-1:2024, Annex A and introduced normalized
tangential force;
— verification and correction of figures;
— update of dimension in Tables 8 to 16.
A list of all parts in the ISO 6626 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
The ISO 6626 series is one of a series of International Standards dealing with piston rings for reciprocating
internal combustion engines. Others are the ISO 6621 series, ISO 6622, ISO 6623, ISO 6624, ISO 6625, the
ISO 6626 series 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, the designer should be aware of the conditions under which
it will be required to operate.

vi
International Standard ISO 6626-2:2024(en)
Internal combustion engines — Piston rings —
Part 2:
Coil-spring-loaded oil control rings of narrow width made of
cast iron
1 Scope
This document specifies the essential dimensional features of coil-spring loaded oil control rings made of
cast iron, types DSF-C, SSF, GSF, DSF, SSF-L, DSF-NG and DSF-CNP. It is applicable to those piston rings in
sizes 60 mm up to 160 mm, inclusive for reciprocating internal combustion engines for road vehicles and
other applications.
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 6621-3, Internal combustion engines — Piston rings — Part 3: Material specifications
ISO 6621-4, Internal combustion engines — Piston rings — Part 4: General specifications
ISO 6621-5, Internal combustion engines — Piston rings — Part 5: Quality requirements
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Overview
The coil-spring loaded oil control ring types are specified in Figures 1 to 8. Their common features and the
features' dimensions are specified in Tables 1 to 5 and shown in Figures 9 to 11. Essential features of coil
springs are shown in Figures 12 to 16. Tables 8 to 16 give the dimensions of coil-spring loaded oil control rings.
The common features and dimensional tables presented in this document constitute a broad range of
variables and, in selecting a particular ring type, the designer shall bear in mind the conditions under which
it will be required to operate.
The designer shall refer to the specifications and requirements of ISO 6621-3 and ISO 6621-4 before
completing a selection.
For the cast iron part, the recommended material is class 10 and shall be in accordance with ISO 6621-3. For
special applications, material classes 20 to 50 may be used.

Variation from these in face design and spring groove may be used, as recommended by individual
manufacturers, in plain or chromed versions.
5 Piston ring types and designation
5.1 Types DFS-C, DFS-CNP, SSF, GSF, DSF, DSF-NG, and SSF-L — General features and
dimensions
See Figure 1 and Tables 8 to 16. Figure 1 is applicable to Figures 2 to 8. Figures 2 to 8 show detailed cross
sections corresponding to Figure 1.
Figure 1 — Types DSF-C, SSF, GSF, DSF, SSF-L, DSF-NG and DSF-CNP
5.2 Type DSF-C ─ Coil-spring loaded bevelled edge oil control ring, chromium plated and
profile ground
5.2.1 General features and dimensions
See Figure 2 and Tables 6 and 7.

Dimensions in millimetres
Key
1 reference plane
a
See Table 3.
b
See Table 4.
c
See Table 5.
d
Angle α and β to be agreed between manufacturer and customer, angles can be different (historical value is 35°).
Figure 2 — Type DSF-C
5.2.2 Designation of a Type DSF-C piston ring in accordance with ISO 6626-2
EXAMPLE Coil-spring loaded bevelled edge oil control ring, chromium plated and profile ground (DSF-C), of
nominal diameter d = 80 mm (80), nominal ring width h = 2,5 mm (2,5), land width h = 0,25 mm (0,25), made of
1 1 5
grey cast iron, non-heat treated, material subclass 11 (MC11), having a selected closed gap of 0,20 mm min. (S020), a
chromium layer thickness on the lands of 0,10 mm (CR2), reduced slot length (WK), a coil spring with reduced heat set
(WF), and a variable pitch with coil diameter d ground (CSE), with tangential force F in accordance with the nominal
7 t
contact pressure p = 1,0 N/mm (PN1,0) and the ring marked with the manufacturer's mark (MM). Parameters in
parenthesis are used in the ISO ring designation:
Piston ring ISO 6626-2 DSF-C - 80 × 2,5 × 0,25 - MC11 / S020 CR2 WK WF CSE PN1,0 MM

5.3 Type DSF-CNP ─ Coil-spring loaded bevelled edge oil control ring, chromium plated not
profile ground
5.3.1 General features and dimensions
See Figure 3 and Tables 8 and 9.
Dimensions in millimetres
Key
1 reference plane
a
See Table 3.
b
See Table 4.
c
See Table 5.
d
Angle α and β to be agreed between manufacturer and customer, angles can be different (historical value is 35°).
e
Before plating.
Figure 3 — Type DSF-CNP
5.3.2 Designation of a Type DSF-CNP piston ring in accordance with ISO 6626-2
EXAMPLE Coil-spring loaded bevelled edge oil control ring, chromium plated not profile ground (DSF-CNP) of
nominal diameter d = 100 mm (100), nominal ring width h = 2,0 mm (2,0), land width h = 0,25 mm (0,25), made of
1 1 5
grey cast iron, non-heat treated, material subclass 12 (MC12), constant spring pitch (CSN) and tangential force F in
t
accordance with the nominal contact pressure p = 1,0 N/mm (PN1,0). Parameters in parenthesis are used in the ISO
ring designation:
Piston ring ISO 6626-2 DSF-CNP- 100 × 2 × 0,25 - MC12 / CSN PN1,0

5.4 Type SSF ─ Coil-spring loaded slotted oil control ring with rectangular groove
5.4.1 General features and dimensions
See Figure 4 and Table 10.
Dimensions in millimetres
Key
1 reference plane
a
See Table 4.
b
See Table 5.
Figure 4 — Type SSF
5.4.2 Designation of a Type SSF piston ring in accordance with ISO 6626-2
EXAMPLE Coil-spring loaded slotted oil control ring with rectangular groove (SSF) of nominal diameter
d = 80 mm (80), nominal ring width h = 2,5 mm (2,5), land width h = 0,50 mm (0,50), made of grey cast iron, non-
1 1 5
heat treated, material subclass 12 (MC12), constant spring pitch (CSN) and tangential force F in accordance with the
t
nominal contact pressure p = 1,0 N/mm (PN1,0). Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6626-2 SSF- 80 × 2,5 × 0,50 - MC12 / CSN PN1,0
5.5 Type GSF ─ Coil-spring loaded double bevelled oil control ring
5.5.1 General features and dimensions
See Figure 5 and Table 11. Top side marking is mandatory in accordance with ISO 6621-4.

Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
a
See Table 4.
b
See Table 5.
Figure 5 — Type GSF
5.5.2 Designation of a Type GSF piston ring in accordance with ISO 6626-2
EXAMPLE Coil-spring loaded double bevelled oil control ring (GSF) of nominal diameter d = 75 mm (75), nominal
ring width h = 2,5 mm (2,5), land width h = 0,30 mm (0,30), made of grey cast iron, non-heat treated, material
1 5
subclass 12 (MC12), with constant spring pitch (CSN) and tangential force F in accordance with the nominal contact
t
pressure p = 1,0 N/mm (PN1,0). Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6626-2 GSF- 75 × 2,5 × 0,30 - MC12 / CSN PN1,0
5.6 Type DSF ─ Coil-spring loaded bevelled edge oil control ring
5.6.1 General features and dimensions
See Figure 6 and Table 11.
Dimensions in millimetres
Key
1 reference plane
a
See Table 4.
b
See Table 5.
Figure 6 — Type DSF
5.6.2 Designation of a Type DSF piston ring in accordance with ISO 6626-2
EXAMPLE Coil-spring loaded bevelled edge oil control ring (DSF) of nominal diameter d = 90 mm (90), nominal
ring width h = 2,5 mm (2,5), land width h = 0,30 mm (0,30), made of grey cast iron, non-heat treated, material
1 5
subclass 12 (MC12), with constant spring pitch (CSN) and tangential force F in accordance with the nominal contact
t
pressure p = 1,0 N/mm (PN1,0). Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6626-2 DSF- 90 × 2,5 × 0,30 - MC12 / CSN PN1,0
5.7 Type DSF-NG ─ Coil-spring loaded bevelled edge oil control ring (face geometry similar
to type DSF-C or type DSF-CNP)
5.7.1 General features and dimensions
See Figure 7 and Tables 12 and 13.

Dimensions in millimetres
Key
1 reference plane
a
See Table 4.
b
See Table 5.
c
Angle α and β to be agreed between manufacturer and customer, angles can be different (historical value is 35°).
Figure 7 — Type DSF-NG
5.7.2 Designation of a Type DSF-NG piston ring in accordance with ISO 6626-2
EXAMPLE Coil-spring loaded bevelled edge oil control ring (DSF-NG) (face geometry similar to type DSF-C or type
DSF-CNP) of nominal diameter d = 80 mm (80), nominal ring width h = 2,0 mm (2,0), land width h = 0,25 mm (0,25),
1 1 5
made of grey cast iron, non-heat treated, material subclass 12 (MC12), constant spring pitch (CSN) and tangential
force F in accordance with the nominal contact pressure p = 1,0 N/mm (PN1,0). Parameters in parenthesis are used
t 0
in the ISO ring designation:
Piston ring ISO 6626-2 DSF-NG - 80 × 2,0 × 0,25 - MC12 / CSN PN1,0
5.8 Type SSF-L ─ Coil-spring loaded slotted oil control ring with rectangular groove at
periphery and V-shaped groove beneath
5.8.1 General features and dimensions
See Figure 8 and Table 14.
Dimensions in millimetres
Key
1 reference plane
a
See Table 4.
b
See Table 5.
c
Angle α and β to be agreed between manufacturer and customer, angles can be different (historical value is 35°).
Figure 8 — Type SSF-L
5.8.2 Designation of a Type SSF-L piston ring in accordance with ISO 6626-2
EXAMPLE Coil-spring loaded slotted oil control ring with rectangular groove at periphery and V-shaped groove
beneath (SSF-L) with 0,4 mm nominal land width of nominal diameter d = 80 mm (80), nominal ring width h = 2,5 mm
1 1
(2,5), land width h = 0,40 mm (0,40), made of grey cast iron, non-heat treated, material subclass 12 (MC12), constant
spring pitch (CSN) and tangential force F in accordance with the nominal contact pressure p = 1,0 N/mm (PN1,0).
t 0
Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6626-2 SSF-L - 80 × 2,5 × 0,40 - MC12 / CSN PN1,0
6 Common features
6.1 Oil drainage by slots or holes
6.1.1 Arrangement of slots
Figure 9 shows the arrangement of oil drainage slots and Table 1 gives the cutter diameter.

a) 8 slots for 60 mm ≤ d < 80 mm b) 10 slots for 80 mm ≤ d < 115 mm
1 1
c) 12 slots for 115 mm ≤ d < 150 mm d) 14 slots for 150 mm ≤ d ≤ 160 mm
1 1
Figure 9 — Arrangement of slots
Table 1 — Cutter diameter
Dimensions in millimetres
Cutter diameter
Nominal diameter
d
d
max.
60 ≤ d < 150 60
150 ≤ d ≤ 160 75
6.1.2 Slot length
6.1.2.1 Standard slot length
Slot length, w , shall be equal to bridge length, w .
1 2
The maximum difference between w and w shall be 4 mm.
1 2
6.1.2.2 Reduced slot length — Code WK
Oil control rings with reduced slot length will retain the same number of slots and the same angular spacing.
The maximum difference between w and w for the standard slot length does not apply.
1 2
See Table 2.
Table 2 — Reduced slot length
Dimensions in millimetres
d w (range of nominal values)
1 1
60 ≤ d < 80 6 . 11
80 ≤ d < 115 8 . 13
115 ≤ d < 150 10 . 15
150 ≤ d ≤ 160 12 … 18
6.1.3 Arrangement of holes
Arrangement of holes is shown in Figure 10. Deviating arrangements shall be agreed between manufacturer
and customer.
Figure 10 — Arrangement of holes
6.1.4 Diameter and number of holes
The diameter (d ) and number (n) of holes shall be agreed between manufacturer and customer.
6.2 Plating thickness — DSF-C and DSF-CNP (coil-spring loaded bevelled edge oil control
ring, chromium plated)
See Figure 11 and Table 3.
Figure 11 — Plating thickness
Table 3 — Plating
...