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ISO/DIS 6624-3
ISO/DIS 6624-3
ISO/DIS 6624-3: Internal combustion engines — Piston rings — Part 3: Keystone rings made of steel

ISO/DIS 6624-3

ISO/TC 22/SC 34

Secretariat: JISC

Date: 2025-12-12

Internal combustion engines — Piston rings —

Voting begins on: 2026-02-06 Voting terminates on: 2026-05-01

Part 3:
Keystone rings made of steel

Voting begins on: 2026-02-06 Voting terminates on: 2026-05-01

Voting begins on: 2026-02-06 Voting terminates on: 2026-05-01

Voting begins on: 2026-02-06 Voting terminates on: 2026-05-01

Moteurs à combustion interne — Segments de piston —

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Partie 3: Segments trapézoïdaux en acier

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DIS stage

© ISO 2025

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.

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Published in Switzerland

Contents

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 Types T, TB, TBA, TM, K, KB, KBA and KM - General features and dimensions 1

5.2 Type T — Straight-faced keystone ring 6° 2

5.3 Type TB — Symmetrical barrel-faced keystone ring 6° 3

5.4 Type TBA — Asymmetrical barrel-faced keystone ring 6° 4

5.5 Type TM — Taper-faced keystone ring 6° 5

5.6 Type K — Straight-faced keystone ring 15° 6

5.7 Type KB — Symmetrical barrel-faced keystone ring 15° 6

5.8 Type KBA — Asymmetrical barrel-faced keystone ring 15° 7

5.9 Type KM — Taper-faced keystone ring 15° 8

6 Common features 9

6.1 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Outside and inside rounded edges 9

6.2 Type T, TB, TBA, TM, K, KB, KBA, KM rings (positive twist type) — Internal bevel top side 10

6.3 Type TM or KM rings with partly cylindrical machined (LM) or lapped (LP) peripheral surface 10

6.4 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Plating or coating configuration 11

7 Force factors 13

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. www.iso.org/directives

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. www.iso.org/patents

Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.

For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO's adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information.

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 6624-3:2017), which has been technically revised.

The main changes compared to the previous edition are as follows:

  • updates were made regarding technology improvements.

A list of all the parts in the ISO 6624 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.

Introduction

The ISO 6624 series is one of a series of International Standards dealing with piston rings for reciprocating internal combustion engines. Others are ISO 6621 series, ISO 6622 series, ISO 6623, ISO 6625, 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 bear in mind the conditions under which it will be required to operate.

It is also essential that the designer refers to the specifications and requirements of ISO 6621-3 and ISO 6621-4 before completing a selection.

Internal combustion engines — Piston rings —

Part 3:
Keystone rings made of steel

1.0 Scope

This document specifies the essential dimensional features of keystone rings made of steel, types T, TB, TBA, TM, K, KB, KBA and KM, having diameters from 70 mm up to and including 160 mm, used in reciprocating internal combustion piston engines.

2.0 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 6621-2, Internal combustion engines — Piston rings — Part 2: Inspection measuring principles

ISO 6621-3, Internal combustion engines — Piston rings — Part 3: Material specifications

ISO 6621-4, Internal combustion engines — Piston rings — Part 4: General specifications

3.0 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/

4.0 Overview

The keystone ring types are specified in Table 1 to Table 3 and Figure 2 to Figure 9. Their common features and the dimensions of those features are specified in Table 4 to Table 10 and Figure 10 to Figure 16. Table 7 and Table 8 give the force factors for the different types of rings, while Table 9 and Table 10 give the dimensions and forces of keystone rings 6° and 15°, respectively.

5.0 Ring types and designation examples

5.1 Types T, TB, TBA, TM, K, KB, KBA and KM - General features and dimensions

Figure 1 is applicable to Figure 2 to Figure 9. Figure 2 to Figure 9 show detailed cross sections corresponding to Figure 1.

Figure 1

5.1.1 Type T — Straight-faced keystone ring 6°

5.1.2 General features

See Table 9 for dimensions and forces.

Dimensions in millimetres

Key

1 reference plane

a Due to manufacturing processing, side angle tolerances are not cumulative.

b Nominal.

Figure 2 — Type T

5.1.3 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 6° keystone ring with straight-faced peripheral surface (T), of nominal diameter d1 = 90 mm (90) and nominal ring width h1 = 2,5 mm (2,5), made of CrSi alloyed steel, subclass 62 (MC 62), and having a fully faced chromium plated peripheral surface with a minimum thickness of 0,1 mm (CR2). Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 T - 90 x 2,5-MC 62/CR2

5.2 Type TB — Symmetrical barrel-faced keystone ring 6°

5.2.1 General features

See Table 9 for dimensions and forces.

Dimensions in millimetres

Key

1 reference plane

a Due to manufacturing processing, side angle tolerances are not cumulative.

b Nominal.

Figure 3 — Type TB

Table 1 — Symmetrical barrel dimensions

h1

h25a

h26

h27

t2, t3b

h8c

Tolerance

2,0

0,40

1,00

±0,30

1,60

0,003...0,015

1,2

2,5

0,45

1,25

±0,40

2,05

1,6

3,0

0,50

1,50

±0,50

2,50

0,005...0,020

2,0

3,5

0,55

1,75

2,95

2,4

4,0

0,60

2,00

±0,60

3,40

0,005...0,023

2,8

a h25 may be lowered for rings with reduced edge dimensions.

b t2 and t3 can be changed as agreed between edge dimensions.

c Gauge width (h8), only informative, may be used only if agreed between the supplier and customer.

5.2.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 6° keystone ring with barrel-faced peripheral surface (TB), of nominal diameter d1 = 90 mm (90) and nominal ring width h1 = 2,5 mm (2,5), made of 11 % Cr minimum martensitic steel, subclass 65 (MC 65), nitrided on the peripheral surface and side faces (NT) to a depth of 0,070 mm min. on the peripheral surface (070), and with an associated side face depth of a minimum of 0,020 mm. Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 TB - 90 x 2,5-MC 65/NT070

5.3 Type TBA — Asymmetrical barrel-faced keystone ring 6°

5.3.1 General features

See Table 9 for dimensions and forces.

Dimensions in millimetres

Key

1 reference plane

2 top side identification mark

a Due to manufacturing processing, side angle tolerances are not cumulative.

b Nominal.

Figure 4 — Type TBA

Table 2 — Asymmetrical barrel dimensions

h1

h25a

h26

h27

t2b

t3b

Tolerance

2,0

0,40

0,60

±0,20

1,5

0...0,007

0,009...0,030

2,5

0,45

0,70

±0,25

1,8

0...0,008

0,011...0,035

3,0

0,55

0,80

2,1

0,012...0,038

3,5

0,60

0,90

±0,30

2,4

0...0,009

0,012...0,040

4,0

0,65

0,95

2,8

0,013...0,045

a h25 may be lowered for rings with reduced edge dimensions.

b t2 and/or t3 or both may be varied as agreed between the supplier and customer.

5.3.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 6° keystone ring with asymmetrical barrel-faced peripheral surface (TBA), of nominal diameter d1 = 90 mm (90) and nominal ring width h1 = 2,5 mm (2,5), made of 17 % Cr minimum martensitic steel, subclass 66 (MC 66), nitrided on the peripheral surface and side faces (NT) to a minimum depth of 0,070 mm on the peripheral surface (070), and with an associated side face depth of a minimum of 0,020 mm. Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 TBA - 90 x 2,5-MC 66/NT070

5.4 Type TM — Taper-faced keystone ring 6°

5.4.1 General features

See Table 9 for dimensions and forces.

Dimensions in millimetres

Key

1 reference plane

2 top side identification mark

a Due to manufacturing processing, side angle tolerances are not cumulative.

b Nominal.

Figure 5 — Type TM

Table 3 — Taper

Code

Taper

Tolerancea

Internal twist feature designs

Tolerancea

M1b

10

M2

M3

M4

M5

30

60

90

120

a For chromium plated rings with a tapered peripheral surface that is not ground, the tolerance shall be increased by 10.

b M1 not for rings with partly cylindrical peripheral surface.

5.4.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 6° keystone ring with 10´ taper-faced peripheral surface (TM1), of nominal diameter d1 = 90 mm (90) and nominal ring width h1 = 2,5 mm (2,5), made of 11 % Cr minimum martensitic steel, subclass 65 (MC 65), and having a fully faced chromium plated peripheral surface with a minimum thickness of 0,1 mm (CR2). Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 ‑ TM1 - 90 x 2,5-MC 65/CR2

5.5 Type K — Straight-faced keystone ring 15°

5.5.1 General features

See Table 10 for dimensions and forces.

Dimensions in millimetres

Key

1 reference plane

a Due to manufacturing processing, side angle tolerances are not cumulative.

b Nominal.

Figure 6 — Type K

5.5.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 15° keystone ring with straight-faced peripheral surface (K), of nominal diameter d1 = 90 mm (90) and nominal ring width h1 = 2,5 mm (2,5), made of CrMoV alloyed steel, subclass 61 (MC 61), and having a fully faced chromium plated peripheral surface with a minimum thickness of 0,1 mm (CR2). Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 K - 90 x 2,5-MC 61/CR2

5.6 Type KB — Symmetrical barrel-faced keystone ring 15°

5.6.1 General features

See Table 1 for symmetrical barrel dimensions. See Table 10 for dimensions and forces.

Dimensions in millimetres

Key

1 reference plane

a Due to manufacturing processing, side angle tolerances are not cumulative.

b Nominal.

Figure 7 — Type KB

5.6.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 15° keystone ring with barrel-faced peripheral surface (KB), of nominal diameter d1 = 90 mm (90) and nominal ring width h1 = 2,5 mm (2,5), made of 17 % Cr minimum martensitic steel, subclass 66 (MC 66), nitrided on the peripheral surface and side faces (NT), to a minimum depth of 0,090 mm on the peripheral surface (090), and with an associated side face depth of a minimum of 0,020 mm. Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 KB- 90 x 2,5-MC 66/NT090

5.7 Type KBA — Asymmetrical barrel-faced keystone ring 15°

5.7.1 General features

See Table 2 for asymmetrical barrel dimensions. See Table 10 for dimensions and forces.

Dimensions in millimetres

Key

1 reference plane

2 top side identification mark

a Due to manufacturing processing, side angle tolerances are not cumulative.

b Nominal.

Figure 8 — Type KBA

5.7.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 15° keystone ring with asymmetrical barrel faced peripheral surface (KBA), of nominal diameter d1 = 90 mm (90) and nominal ring width h1 = 2,5 mm (2,5), made of 17 % Cr minimum martensitic steel, subclass 66 (MC 66), nitrided on the peripheral surface and side faces (NT), to a depth of 0,070 mm min. on the peripheral surface (070), and with an associated side face depth of a minimum of 0,020 mm. Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 KBA - 90 x 2,5-MC 66/NT070

5.8 Type KM — Taper-faced keystone ring 15°

5.8.1 General features

See Table 3 for taper. See Table 10 for dimensions and forces.

Dimensions in millimetres

Key

1 reference plane

2 top side identification mark

a Due to manufacturing processing, side angle tolerances are not cumulative.

b Nominal.

Figure 9 — Type KM

5.8.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 15° keystone ring with 10´ taper-faced peripheral surface (KM1), of nominal diameter d1 = 90 mm (90) and nominal ring width h1 = 2,5 mm (2,5), made of CrMoV alloyed steel, subclass 61 (MC 61), and having a fully faced chromium plated peripheral surface with a minimum thickness 0,1 mm (CR2). Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 KM1- 90 x 2,5-MC 61/CR2

6.0 Common features

6.1 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Outside and inside rounded edges

Outside and inside rounded edges are shown in Figure 10 and Figure 11; their dimensions are given in Table 4.

Figure 10 — Outside and inside rounded edges

Figure 11 — Details of Figure 10

Table 4 — hx and hy dimensions

h1

hx

hy

max.

max.

2 ≤ h1 < 2,5

0,3

0,35

h1 ≥ 2,5

0,3

0,4

6.1.1 Type T, TB, TBA, TM, K, KB, KBA, KM rings (positive twist type) — Internal bevel top side

An internal bevel is not recommended for the 15° keystone rings with ring width h1 given in the "nominal value of ring width" column 1 of Table 10.

Key

1 top side identification mark

Figure 12 — Internal bevel top side (IF)

Table 5 — a3 dimensions

d1

a3

Tolerance

70 ≤ d1 ≤ 160

0,8 × a1

6.1.2 Type TM or KM rings with partly cylindrical machined (LM) or lapped (LP) peripheral surface

Taper M1 is excluded.

Key

1 top side identification mark

Figure 13 — Partly cylindrical peripheral surface

Table 6 — h24 dimensions

h1

h24
max.

h24
max.

each side of gap up to 30°

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

Partly cylindrical peripheral surfaces shall be visible.

6.1.3 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Plating or coating configuration

6.1.4 Chromium plated or spray coated rings

Coating thickness is defined on ISO6621-4.

General

Semi-inlaid types are not recommended.

Fully faced

See Figure 14.

a) T or K rings

b) TB or KB rings

c) TBA or KBA rings

d) TM or KM rings

Figure 14 — Fully faced rings

Inlaid

Inlaid types are not recommended for chromium plated rings. See Figure 15.

a) T or K rings

b) TB or KB rings

c) TBA or KBA rings

d) TM or KM rings

Figure 15 — Inlaid rings

6.1.5 Nitrided surface

Case depth is defined on ISO6621-4.

6.1.6 PVD rings

Coating thickness is defined on ISO6621-4.

a) TB or KB rings

b) TBA or KBA rings

c) TM or KM rings

Figure 16 — PVD rings

7.0 Force factors

The tangential and diametral forces given in Table 9 and Table 10 shall be corrected when additional features are used.

The force correction factor for the ratio m/(d1 – a1) given in ISO 6621-4 shall be used.

For common features, the multiplier correction factors given in Table 7 and Table 8 shall be used.

Table 7 — Force correction factors for T, TB, TBA, TM, K, KB, KBA and KM rings with features IF and taper

Factor

M2 or M3

M4 or M5

IF

0,98

0,96

0,88

Table 8 — Force correction factors for chromium plated, spray coated, PVD coated or nitrided T, TB, TBA, TM, K, KB, KBA and KM rings

d1

Factor

mm

CRF / PC001 … PC030

CR1 / PC040

CR2/SC1

CR3/SC2

CR4/SC3

SC4

NP030 ... NP130 NT030 ... NT130

70 ≤ d1 < 100

1

0,91

0,86

0,82

0,78

0,74

1,03

100 ≤ d1 < 125

1

0,93

0,89

0,86

0,82

0,79

125 ≤ d1 ≤ 160

1

0,94

0,91

0,89

0,86

0,83

Table 9 — Dimensions of T, TB, TBA, TM keystone rings 6°

Nominal diametera

Radial wall thickness

Nominal value
of ring widthb

Keystone ring width

Closed gap

Tangential force
Ft [N]

Diametral force
Fd [N]

Method A

Method B

Measured value

Measured value

d1

a1

h1

a6

h3

h3

s1

h1

h1

Tolerance

1

2

1

2

1

2

a6

Tolerance

1

2

Tolerance

1

2

Tolerance

70

10,4

13,2

22,3

28,4

71

10,3

13,1

22,0

28,1

72

2,5

0,20

10,1

12,9

21,8

27,7

73

10,0

12,7

21,5

27,4

74

11,4

14,6

24,6

31,3

75

1,832

0

-0,024

For phosphated PO surface:

+0,010

–0,024

2,332

0

-0,024

For phosphated PO surface:

+0,010

–0,024

1,61

0

-0,22

For phosphated PO surface:

+0,09

–0,22

11,3

14,4

24,3

31,0

76

2,7

11,1

14,1

23,8

30,3

77

10,8

13,8

23,2

29,6

78

10,7

13,6

23,0

29,3

79

12,1

15,4

26,0

33,2

80

2,0

2,5

1,5

1,8

2,32

12,0

15,3

±30 % if

25,7

32,8

±30 % if

81

2,9

±0,15

11,8

15,1

Ft <10 N

25,5

32,5

Fd < 21,5 N

82

0,25

+0,15

0

11,7

15,0

25,2

32,2

83

Within

11,6

14,8

24,9

31,8

84

a ring:

11,4

14,5

24,4

31,2

85

13,0

16,6

27,9

35,7

86

0,15 max.

12,9

16,5

±20 % if

27,7

35,4

±20 % if

87

3,1

12,6

16,1

Ft ≥ 10 N

27,1

34,7

Fd ≥ 21,5 N

88

12,5

16,0

26,9

34,4

89

12,3

15,7

26,3

33,7

90

2,278

0

-0,024

For phosphated PO surface:

+0,010

–0,024

2,778

0

-0,024

For phosphated PO surface:

+0,010

–0,024

2,08

0

-0,22

For phosphated PO surface:

+0,09

–0,22

15,5

18,9

33,4

40,7

91

17,7

21,6

38,1

46,4

92

17,3

21,1

37,2

45,4

93

3,3

17,0

20,8

36,7

44,7

94

16,7

20,3

35,8

43,6

95

2,5

3,0

2,0

2,27

2,77

0,30

16,3

19,8

34,9

42,6

96

18,5

22,6

39,9

48,6

97

18,3

22,3

39,3

48,0

98

3,5

18,0

22,0

38,7

47,3

99

17,8

21,7

38,2

46,6

100

17,5

21,3

37,6

45,8

101

2,278

2,778

2,08

17,2

21,0

37,1

45,2

102

0

0

0

19,7

24,0

42,3

51,6

103

–0,024

–0,024

–0,22

19,3

23,6

41,6

50,7

104

3,7

2,27

2,77

0,30

19,1

23,3

41,1

50,1

105

For phosphated PO surface:

+0,010

–0,024

For phosphated PO surface:

+0,010

–0,024

For phosphated PO surface:

+0,09

–0,22

18,8

22,9

40,3

49,2

106

18,5

22,6

39,8

48,6

107

2,5

3,0

2,0

18,2

22,2

39,1

47,7

108

20,7

25,3

44,5

54,4

109

20,3

24,8

43,6

53,2

110

3,9

±0,20

19,8

24,2

42,6

52,1

111

19,4

23,7

±30 % if

41,6

50,9

±30 % if

112

Within

18,9

23,1

Ft <10 N

40,6

49,7

Fd < 21,5 N

113

a ring:

21,5

26,3

46,3

56,6

114

+0,15

0

21,2

26,0

45,7

55,9

115

4,1

0,20 max.

20,9

25,6

44,9

54,9

116

20,5

25,1

44,1

54,0

117

0,35

20,2

24,7

±20 % if

43,4

53,0

±20 % if

118

19,8

24,2

Ft ≥ 10 N

42,6

52,1

Fd ≥ 21,5 N

119

22,6

27,7

48,6

59,5

120

22,2

27,2

47,8

58,5

121

21,9

26,8

47,0

57,6

122

4,3

21,5

26,3

46,2

56,6

123

21,1

25,9

45,5

55,7

124

20,8

25,5

44,7

54,7

125

2,724

0

–0,024

For phosphated PO surface:

+0,010

–0,024

3,224

0

–0,024

For phosphated PO surface:

+0,010

–0,024

2,63

0

–0,22

For phosphated PO surface:

+0,09

–0,22

29,0

34,3

62,3

73,8

126

28,3

33,5

60,9

72,1

127

4,5

27,7

32,7

59,5

70,4

128

27,0

32,0

58,0

68,7

129

3,0

3,5

2,5

2,71

3,21

26,3

31,2

56,6

67,1

130

29,9

35,5

64,4

76,3

131

0,40

29,5

35,0

63,4

75,2

132

4,7

29,0

34,3

62,3

73,8

133

28,5

33,8

61,3

72,7

134

28,0

33,2

60,2

71,3

135

2,724

0

–0,024

For phosphated PO surface:

+0,010

–0,024

3,224

0

–0,024

For phosphated PO surface:

+0,010

–0,024

2,63

0

–0,22

For phosphated PO surface:

+0,09

–0,22

27,4

32,5

59,0

69,9

136

31,2

37,0

67,2

79,6

137

30,7

36,4

66,0

78,2

138

4,9

30,2

35,7

64,8

76,9

139

0,40

+0,15

0

29,6

35,1

63,7

75,5

140

29,1

34,5

62,5

74,1

141

28,5

33,8

±30 % if

61,3

72,7

±30 % if

142

32,4

38,5

Ft < 10 N

69,7

82,7

Fd < 21,5 N

143

31,9

37,8

68,5

81,3

144

5,1

±0,20

31,3

37,2

67,3

79,9

145

3,0

3,5

2,5

2,71

3,21

30,8

36,5

66,2

78,5

146

Within

30,2

35,9

65,0

77,1

147

a ring:

29,6

35,1

63,6

75,5

148

0,20 max.

33,7

40,0

±20 % if

72,4

86,0

±20 % if

149

32,9

39,1

Ft ≥ 10 N

70,8

84,0

Fd ≥ 21,5 N

150

5,3

32,1

38,2

69,1

82,1

151

2,724

3,224

2,63

31,3

37,1

67,2

79,9

152

0

0

0

30,5

36,2

65,6

77,9

153

–0,029

–0,029

–0,26

34,7

41,2

74,6

88,6

154

For phosphated PO surface:

+0,010

–0,029

For phosphated PO surface:

+0,010

–0,029

For phosphated PO surface:

+0,09

–0,27

+0,20

0

34,0

40,5

73,2

87,0

155

5,5

0,50

33,4

39,7

71,8

85,3

156

32,9

39,1

70,7

84,0

157

32,2

38,3

69,3

82,3

158

31,6

37,5

67,9

80,7

159

35,8

42,6

77,0

91,6

160

5,7

35,0

41,6

75,2

89,4

a For intermediate sizes (e.g. repair sizes), the radial wall thickness of the next smaller nominal diameter should be applied.

b Additional ring widths can be agreed between supplier and customer.

NOTE 1 The values for Ft and Fd given in Table 9 apply to steel with a typical modulus of elasticity (En) of 210 GN/m2. Multiplying factors are given in ISO 6621-4. Mean forces are calculated for nominal radial wall thickness (a1) and mean trapezoidal ring width (h3).

NOTE 2 For the sole purpose of this document, the assumed average ratio Fd/Ft is 2,15.

NOTE 3 For measurement of keystone ring width, see ISO 6621-2.

NOTE 4 Columns 1 and 2 of nominal value of ring width, h1, are the basis for the two columns for h3, method A and B, for Ft and Fd.

Table 10 — Dimensions of K, KB, KBA, KM keystone rings 15°

Nominal diametera

Radial wall thickness

Nominal value
of ring widthb

Keystone ring width

Closed gap

Tangential force
Ft [N]

Diametral force
Fd [N]

Method A

Method B

Measured value

Measured value

d1

a1

h1

a6

h3

h3

s1

h1

h1

Tolerance

1

2

1

2

1

2

a6

Tolerance

1

2

Tolerance

1

2

Tolerance

70

11,9

14,7

25,6

31,7

71

2,5

11,8

14,6

25,3

31,3

72

0,20

11,6

14,4

25,0

30,9

73

11,5

14,2

24,7

30,6

74

13,0

16,2

27,9

34,7

75

12,9

16,0

27,6

34,4

76

2,7

12,6

15,6

27,0

33,6

77

12,3

15,3

26,4

32,9

78

12,2

15,1

26,1

32,5

79

2,097

2,597

1,49

13,6

17,0

29,3

36,6

80

0

0

0

13,5

16,8

±30 % if

29,0

36,2

±30 % if

81

2,9

–0,029

–0,029

–0,11

13,4

16,7

Ft < 10 N

28,7

35,8

Fd < 21,5 N

82

For phosphated PO surface:

+0,010

–0,029

For phosphated PO surface:

+0,010

–0,029

2,10

2,60

For phosphated PO surface:

+0,04

–0,11

0,25

13,2

16,5

28,4

35,5

83

13,1

16,3

28,2

35,1

84

±0,15

+0,15

0

12,8

16,0

27,6

34,4

85

2,5

3,0

1,5

14,5

18,2

±20 % if

31,3

39,1

±20 % if

86

Within

14,4

18,0

Ft ≥ 10 N

31,0

38,7

Fd ≥ 21,5 N

87

3,1

a ring:

14,1

17,7

30,4

38,0

88

0,15 max.

14,0

17,5

30,1

37,6

89

13,7

17,2

29,5

36,9

90

13,6

17,0

29,2

36,6

91

15,4

19,3

33,0

41,4

92

15,0

18,8

32,3

40,5

93

3,3

14,8

18,5

31,8

39,9

94

14,4

18,1

31,0

39,0

95

0,30

14,1

17,7

30,3

38,0

96

15,9

20,0

34,2

43,1

97

15,7

19,8

33,7

42,5

98

3,5

15,5

19,5

33,2

41,9

99

15,2

19,2

32,8

41,3

100

18,8

22,7

40,5

48,8

101

18,6

22,4

40,0

48,2

102

21,1

25,5

45,3

54,7

103

2,463

2,963

2,05

0,30

20,7

25,0

44,5

53,8

104

3,7

0

0

0

20,5

24,7

44,0

53,2

105

–0,034

–0,034

2,45

2,95

–0,13

20,1

24,3

43,2

52,2

106

For phosphated PO surface:

+0,010

–0,034

For phosphated PO surface:

+0,010

–0,034

For phosphated PO surface:

+0,04

–0,13

19,9

24,0

42,7

51,6

107

19,5

23,5

41,9

50,6

108

22,0

26,7

47,4

57,4

109

21,5

26,1

46,3

56,1

110

3,9

3,0

3,5

2,0

21,1

25,5

45,3

54,9

111

20,6

24,9

44,3

53,6

112

20,1

24,3

43,2

52,3

113

22,7

27,6

48,8

59,3

114

22,4

27,2

±30 % if

48,2

58,5

±30 % if

115

4,1

±0,20

22,1

26,8

Ft < 10 N

47,4

57,5

Fd < 21,5 N

116

+0,15

0

21,7

26,3

46,6

56,5

117

Within

21,3

25,8

45,8

55,6

118

a ring:

0,35

20,9

25,4

44,9

54,6

119

0,20 max.

23,7

28,8

50,9

61,9

120

23,3

28,3

±20 % if

50,0

60,9

±20 % if

121

22,9

27,9

Ft ≥ 10 N

49,2

59,9

Fd ≥ 21,5 N

122

4,3

22,5

27,4

48,4

58,9

123

22,1

27,0

47,6

57,9

124

21,8

26,5

46,8

57,0

125

2,830

0

–0,034

For phosphated PO surface:

+0,010

–0,034

3,330

0

–0,034

For phosphated PO surface:

+0,010

–0,034

2,61

0

–0,13

For phosphated PO surface:

+0,04

–0,13

30,0

35,3

64,4

76,0

126

29,3

34,5

63,0

74,3

127

4,5

28,6

33,7

61,5

72,5

128

27,9

32,9

60,0

70,8

129

3,5

4,0

2,5

2,80

3,30

27,2

32,1

58,6

69,1

130

30,8

36,4

66,2

78,2

131

0,40

30,3

35,8

65,2

77,0

132

4,7

29,8

35,2

64,0

75,6

133

29,3

34,6

63,0

74,5

134

28,8

34,0

61,8

73,0

135

28,2

33,3

60,6

71,6

136

31,9

37,7

68,5

81,2

137

31,3

37,1

67,4

79,7

138

4,9

30,8

36,4

66,2

78,3

139

0,40

+0,15

0

30,2

35,8

65,0

76,9

140

29,7

35,1

63,8

75,5

141

29,1

34,5

62,6

74,1

142

2,830

0

–0,034

For phosphated PO surface:

+0,010

–0,034

3,330

0

–0,034

For phosphated PO surface:

+0,010

–0,034

2,61

0

–0,13

For phosphated PO surface:

+0,04

–0,13

32,8

39,0

±30 % if

70,6

83,8

±30 % if

143

32,3

38,3

Ft < 10 N

69,4

82,4

Fd < 21,5 N

144

5,1

31,7

37,7

68,3

81,0

145

±0,20

31,2

37,0

67,1

79,6

146

3,5

4,0

2,5

2,80

3,30

30,6

36,4

65,9

78,2

147

Within

30,0

35,6

64,5

76,5

148

a ring:

33,9

40,3

±20 % if

72,9

86,6

±20 % if

149

0,20 max.

33,1

39,4

Ft ≥ 10 N

71,2

84,7

Fd ≥ 21,5 N

150

5,3

32,4

38,5

69,6

82,7

151

31,5

37,4

67,7

80,5

152

30,7

36,5

66,1

78,6

153

34,7

41,3

74,6

88,8

154

34,0

40,5

73,2

87,2

155

5,5

0,50

+0,20

0

33,4

39,8

71,8

85,5

156

32,9

39,1

70,6

84,1

157

32,2

38,4

69,2

82,5

158

31,6

37,6

67,9

80,8

159

35,5

42,4

76,4

91,2

160

5,7

34,7

41,4

74,6

89,1

a For intermediate sizes (e.g. repair sizes), the radial wall thickness of the next smaller nominal diameter should be applied.

b Additional ring widths can be agreed between supplier and customer.

NOTE 1 The values for Ft and Fd given in Table 10 apply to steel with a typical modulus of elasticity (En) of 210 GN/m2. Multiplying factors are given in ISO 6621-4. Mean forces are calculated for nominal radial wall thickness (a1) and mean trapezoidal ring width (h3).

NOTE 2 For the sole purpose of this document, the assumed average ratio Fd/Ft is 2,15.

NOTE 3 For measurement of keystone ring width, see ISO 6621-2.

NOTE 4 Columns 1 and 2 of nominal value of ring width, h1, are the basis for the two columns for h3, method A and B, for Ft and Fd.

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