ISO 13050:2014

INTERNATIONAL ISO
STANDARD 13050
Second edition
2014-12-01
Corrected version
2016-04-01
Synchronous belt drives — Metric
pitch, curvilinear profile systems G, H,
R and S, belts and pulleys
Transmissions synchrones — Pas métrique, systèmes à denture
curviligne G, H, R et S, courroies et poulies
Reference number
©
ISO 2014
© ISO 2014, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2014 – All rights reserved

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Synchronous belt drive system types . 2
4 Belt nomenclature . 3
5 Pulley nomenclature . 3
6 Profile system G . 4
6.1 Belt dimensions and tolerances . 4
6.1.1 Belt tooth dimensions . 4
6.1.2 Belt widths and tolerances . 5
6.1.3 Pitch length measurement . 5
6.2 Pulleys, profile system G . 7
6.2.1 General. 7
6.2.2 Generating tool rack . . 7
6.2.3 Pulley groove profile dimensions and tolerances . 9
6.2.4 Pulley outside diameters .10
6.2.5 Pulley width .12
7 Profile system H .13
7.1 Belt dimensions and tolerances .13
7.1.1 Belt tooth dimensions .13
7.1.2 Belt widths and tolerances .14
7.1.3 Pitch length measurement .15
7.1.4 Procedure .15
7.2 Pulleys, profile system H .17
7.2.1 General.17
7.2.2 Generating tool rack . .17
7.2.3 Pulley groove profile dimensions and tolerances .19
7.2.4 Pulley outside diameters .21
7.2.5 Pulley width .24
8 Profile system R .25
8.1 Belt dimensions and tolerances .25
8.1.1 Belt tooth dimensions .25
8.1.2 Belt widths and tolerances .26
8.1.3 Pitch length measurement .26
8.2 Pulleys, profile system R .29
8.2.1 General.29
8.2.2 Generating tool rack . .29
8.2.3 Pulley groove profile dimensions and tolerances .31
8.2.4 Pulley outside diameters .32
8.2.5 Pulley width .35
9 Profile system S .38
9.1 Belt dimensions and tolerances .38
9.1.1 Belt tooth dimensions .38
9.1.2 Belt widths and tolerances .39
9.1.3 Pitch length measurement .39
9.2 Pulleys, profile system S .41
9.2.1 General.41
9.2.2 Generating tool rack . .42
9.2.3 Pulley groove profile dimensions and tolerances .43
9.2.4 Pulley outside diameters .44
9.2.5 Pulley width .45
Annex A (normative) Belt pitch lengths and tolerances .47
Annex B (normative) Relationship between centre distance and belt pitch length .49
Annex C (normative) Pulley tolerances .50
Annex D (normative) Flange dimensions .53
Bibliography .54
iv © ISO 2014 – All rights reserved

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).
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/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
The committee responsible for this document is ISO/TC 41, Belts and pulleys (including veebelts),
Subcommittee SC 4, Synchronous belt drives.
This second edition cancels and replaces the first edition (ISO 13050:1999), which has been technically
revised.
This corrected version of ISO 13050:2014 incorporates the following corrections: in Formulas (1) and
(2), “Ao” has been added before the first square bracket in each equation.
INTERNATIONAL STANDARD ISO 13050:2014(E)
Synchronous belt drives — Metric pitch, curvilinear profile
systems G, H, R and S, belts and pulleys
1 Scope
This International Standard specifies the principal characteristics of metric pitch curvilinear
synchronous endless belts and pulleys in G, H, R, and S profile systems for use in synchronous belt
drives (also known in the past as timing belt drives, positive belt drives, gear belt drives) for mechanical
power transmission and where positive indexing or synchronization might be required.
The principal belt and pulley characteristics include the following:
a) nominal belt tooth dimensions;
b) belt tooth pitch spacing;
c) belt length and width dimensions and tolerances;
d) belt length measurement specifications;
e) pulley groove dimensions and tolerances;
f) pulley diameter and width dimensions and tolerances;
g) pulley quality specification.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 254, Belt drives — Pulleys — Quality, finish and balance
3 Synchronous belt drive system types
Four profile systems and 14 profiles for curvilinear synchronous drives are standardized.
Profile system G Profile system R
Profile G8M Profile R3M
(Tooth/groove pitch 8mm) (Tooth/groove pitch 3mm)
Profile G14M Profile R5M
(Tooth/groove pitch 14mm) (Tooth/groove pitch 5mm)
Profile R8M
(Tooth/groove pitch 8mm)
Profile R14M
(Tooth/groove pitch 14mm)
Profile R20M
(Tooth/groove pitch 20mm)
Profile system H Profile system S
Profile H3M Profile S8M
(Tooth/groove pitch 3mm) (Tooth/groove pitch 8mm)
Profile H5M Profile S14M
(Tooth/groove pitch 5mm) (Tooth/groove pitch 14mm)
Profile H8M
(Tooth/groove pitch 8mm)
Profile H14M
(Tooth/groove pitch 14mm)
Profile H20M
(Tooth/groove pitch 20mm)
2 © ISO 2014 – All rights reserved

4 Belt nomenclature
A belt is identified as follows:
a) the belt length or pitch length in millimetres, e.g. 1 400 mm;
b) the profile system, e.g. “G”,“H”, “R”, or “S”;
c) the pitch or tooth pitch in millimetres, e.g. 14 mm;
d) the width or belt width in millimetres, e.g. 40 mm (for profile system S, the width in millimetres × 10);
e) double-sided belts are designated by adding the letter “D” before the designation of the profile system.
EXAMPLE A synchronous belt in the above profile systems of 1 400 mm length, 14 mm pitch, and 40 mm
wide is identified as follows:
Profile system G Profile system R
1400-G14M-40 1400-R14M-40
1400-DG14M-40 1400-DR14M-40
Profile system H Profile system S
1400-H14M-40 1400-S14M-400
1400-DH14M-40 1400-DS14M-400
5 Pulley nomenclature
A pulley is identified as follows:
a) the letter “P” indicates a pulley;
b) the number of grooves, e.g. 30;
c) the profile system, e.g. “G“, “H”, “R”, or “S”;
d) the pitch or groove pitch in millimetres, e.g. 14 mm;
e) the width or belt width in millimetres, e.g. 40 mm (for profile system S, the width in millimetres × 10).
EXAMPLE A pulley in the above profile systems of 30 grooves, 14 mm pitch, and 40 mm wide is identified as
follows:
Profile system G Profile system R
P30-G14M-40 P30-R14M-40
Profile system H Profile system S
P30-H14M-40 P30-S14M-400
6 Profile system G
6.1 Belt dimensions and tolerances
6.1.1 Belt tooth dimensions
The nominal belt tooth dimensions are given in Table 1 and shown in Figure 1.
Table 1 — Nominal tooth dimensions
Dimensions in millimetres
a
Profile Belt pitch b h R1 Ao a xo L1
g g
G8M 8 5,200 3,43 0,74 2,29 0,80 0,379 1,378
G14M 14 9,100 6,00 1,30 4,00 1,40 0,661 2,422
a
a is the belt design pitch differential.

R1
a
b
g xo
h
g
Y
Ao
L1
X
Figure 1 — Tooth dimensions — Profile system G
4 © ISO 2014 – All rights reserved

Detail of tooth face
For Ao ≥ x ≥ xo:
 
 
yA=+oI nA ox//Ao xx−11 −− / Ao  (1)
() ()
 
 
 
 
where
xo corresponds to y = hg;
L1 is equal to bg − 2(Ao − xo).
NOTE 1 Indicated base tooth profile remains constant in all parts.
NOTE 2 “O” reference points remain in contact with the part outer surface generated by part radius of
curvature.
NOTE 3 Groove profile bottom surface in circular part form is an arc whose chordal distance is L1 and whose
radius originates at the part centre.
6.1.2 Belt widths and tolerances
Belt widths and tolerances are given in Table 2.
Table 2 — Widths and width tolerances
Dimensions in millimetres
Tolerance on width for belt pitch lengths
Over 840 mm and
Profile Nominal belt width
Up to and including Over
up to and including
840 mm 1 680 mm
1 680 mm
12 +0,8 −0,8 +0,8 −1,2 +0,8 −1,2
21 +0,8 −0,8 +0,8 −1,2 +0,8 −1,2
G8M
36 +0,8 −0,8 +0,8 −1,2 +0,8 −1,2
62 +1,2 −1,2 +1,2 −1,6 +1,6 −1,6
20 +0,8 −0,8 +0,8 −1,2 +0,8 −1,2
37 +0,8 −0,8 +0,8 −1,2 +0,8 −1,2
G14M 68 +1,2 −1,6 +1,6 −1,6 +1,6 −2,0
90 +1,6 −1,6 +1,6 −2,0 +2,0 −2,0
125 +2,4 −2,4 +2,4 −2,8 +2,4 −3,2
6.1.3 Pitch length measurement
See Annex A for tolerances and Annex B for the relationship between the centre distance and the belt
pitch length.
6.1.3.1 Measuring fixture (see Figure 3)
The pitch length of a synchronous belt shall be determined by placing the belt on a measuring fixture
composed of the following elements.
6.1.3.1.1 Two pulleys of equal diameter, as specified in Table 3, of the proper belt profile and having
standard tooth space dimensions. These pulleys should be made to the tolerances shown in Table 3. One
pulley shall be free to rotate on a fixed-position shaft, while the other shall be free to rotate on a moveable
shaft to permit the centre distance to change.
6.1.3.1.2 Means of applying a total measuring force to the moveable pulley.
6.1.3.1.3 Means of measuring the centre distance between the two pulleys with the necessary
degree of accuracy for centre distance measurement.
6.1.3.2 Total measuring force
The total measuring force to be applied for measuring belts is given in Table 4.
6.1.3.3 Procedure
In measuring the pitch length of a synchronous belt, the belt should be rotated at least two revolutions
to seat it properly and to divide the total force equally between the two spans of the belt. The pitch
length shall be calculated by adding the pitch circumference of one of the pulleys to twice the measured
centre distance.
Key
1 centre distance
2 total measuring force
Figure 2 — Diagram of fixture for measuring pitch length
Table 3 — Belt length measuring pulleys
Dimensions in millimetres
Radial Axial
Number of Pitch circumfer- Outside diame-
runout runout
Profile
a
grooves ence ter
b b
F.I.M. F.I.M.
84,980
G8M 34 272 0,013 0,025
±0,013
175,454
G14M 40 560 0,013 0,051
±0,025
a
Pulleys outside of the diameter tolerance range specified can be used if the resulting belt length measurements are
corrected for the actual pulley diameters.
b
Full indicator movement.
NOTE The number of pulley teeth specified in Table 3 determines the recommended sizes for measuring the
belt pitch length. Practically, other sizes of pulleys could be used provided they have the same number of teeth,
and meet the dimensional requirements of Table 3.
6 © ISO 2014 – All rights reserved

Table 4 — Total measuring force
Forces in newtons
Belt width
mm
Profile
12 20 21 36 37 62 68 90 125
G8M 267 — 467 756 — 1223 — — —
G14M — 1179 — — 2046 — 3447 4315 5627
6.2 Pulleys, profile system G
6.2.1 General
See Annex C for tolerances.
The pulley is characterized by a curvilinear groove profile. This groove profile is defined as the profile
formed by the generating tool rack form required to machine-finish the curvilinear profile. The profile
is different for each pulley diameter, but can be closely approximated by a nominal groove profile over
specified ranges of number of grooves.
6.2.2 Generating tool rack
Dimensions and tolerances for the generating tool rack for pulleys with profile system G are given in
Table 5 and shown in Figure 3.
P
b
(0,0) P0
X
X
P1
X
P2
r1
X
r4 P3
r2
r3
h
r5
r
X
P4
r6
X
P5
r7
X
P6
r8
X
X P7
P8
X
Figure 3 — Pulley generating tool rack dimensions

8 © ISO 2014 – All rights reserved
Table 5 — Pulley generating tool rack dimensions
Dimensions in millimetres
Profile Number P h P r P r P r P r P r P r P r P r P X
b r 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8
of grooves
(X,Y) (X,Y) (X,Y) (X,Y) (X,Y) (X,Y) (X,Y) (X,Y) (X,Y)
22 to 27 7,784 3,541 3,480 0,842 2,710 1,459 2,567 — — 8,833 2,427 5,882 1,841 3,123 1,324 1,450 0,979 0,552 0,856 0,856
0 −0,433 −0,788 −1,275 −2,580 −3,235 −3,491 −3,541
28 to 37 7,843 3,513 3,448 0,828 2,746 1,086 2,578 — — 9,487 2,447 5,901 1,894 3,152 1,367 1,505 1,009 0,640 0,843 0,843
0 −0,348 −0,715 −1,193 −2,486 −3,177 −3,447 −3,513
38 to 58 7,891 3,487 3,426 0,819 2,829 0,918 2,583 — — 9,964 2,462 5,921 1,940 3,181 1,410 1,562 1,024 0,669 0,831 0,831
G8M
0 −0,232 −0,668 −1,126 −2,402 −3,119 −3,414 −3,487
59 to 89 7,930 3,467 3,412 0,818 2,943 0,846 2,586 — — 10,385 2,470 5,932 1,978 3,205 1,443 1,614 1,039 0,725 0,820 0,820
0 −0,130 −0,632 −1,082 −2,328 −3,072 −3,384 −3,467
90 to 250 8,040 3,452 3,558 0,846 3,040 0,957 2,751 1,984 2,617 8,275 2,345 5,111 1,978 3,042 1,559 1,725 1,181 0,805 0,951 0,951
0 −0,164 −0,512 −0,873 −1,724 −2,495 −3,056 −3,359 −3,452
27 to 29 13,674 6,174 6,009 1,461 4,777 2,188 4,536 9,728 4,405 11,867 3,768 9,625 3,161 6,114 2,486 3,338 1,808 1,511 1,505 1,505
0 −0,684 −1,222 −1,696 −3,487 −4,619 −5,489 −6,041 −6,174
30 to 35 13,725 6,147 5,986 1,453 4,738 2,206 4,519 9,448 4,418 11,919 3,800 9,584 3,213 6,129 2,522 3,433 1,850 1,588 1,496 1,496
0 −0,717 −1,244 −1,626 −3,408 −4,531 −5,436 −5,990 −6,147
36 to 45 13,780 6,117 5,961 1,446 4,685 2,241 4,490 — — 13,051 3,951 10,115 3,297 6,163 2,582 3,489 1,883 1,672 1,485 1,485
0 −0,780 −1,312 −3,041 −4,387 −5,356 −5,942 −6,117
46 to 60 13,831 6,090 5,940 1,437 4,652 2,180 4,484 — — 13,091 3,971 10,092 3,417 6,222 2,649 3,541 1,913 1,745 1,476 1,476
G14M
0 −0,815 −1,313 −2,983 −4,172 −5,267 −5,899 −6,090
61 to 90 13,879 6,065 5,9190 1,429 4,608 2,151 4,484 — — 13,183 3,988 10,067 3,463 6,236 2,702 3,586 1,940 1,812 1,467 1,467
−0,883 −1,285 −2,928 −4,081 −5,193 −5,857 −6,065
91 to 149 13,927 6,040 5,900 1,420 4,568 2,586 4,476 — — 13,304 4,014 10,051 3,505 6,245 2,746 3,629 1,969 1,872 1,458 1,458
0 −0,955 −1,292 −2,848 −3,997 −5,128 −5,815 −6,040
150 to 250 13,956 6,024 5,887 1,414 4,537 5,757 4,458 — — 13,150 4,030 10,051 3,533 6,249 2,701 3,652 1,983 1,908 1,453 1,453
0 −1,031 −1,352 −2,799 −3,938 −5,171 −5,792 −6,024

6.2.3 Pulley groove profile dimensions and tolerances
Dimensions and tolerances for the pulley groove profile for G8M and G14M pulleys are given in Table 6
and shown in Figures 4 and 5.
Table 6 — Pulley groove profile dimensions
Dimensions in millimetres
Profile Number of b h R Ao xo L1 a
g g 1
grooves
G8M 22 to 89 5,400 3,43 0,80 2,29 0,379 1,60 0,80
90 to 250 5,660 3,43 0,80 2,29 0,379 1,60
G14M 28 to over 9,450 6,00 1,40 4,00 0,661 2,80 1,40
xo
b
g
R1
h
g
Y
X
Ao
L1
Figure 4 — Pulley groove profile
For Ao ≥ x ≥ xo:
 
 
yA=+oI nAox//Ao xx−11−− / Ao  (2)
 
() ()
 
 
 
 
where
xo corresponds to y = hg;
L1 is equal to bg − 2(Ao − xo).
NOTE 1 Indicated base tooth profile remains constant in all parts.
NOTE 2 “O” Reference points remain in contact with the part outer surface generated by part radius of
curvature.
NOTE 3 Groove profile bottom surface in circular part form is an arc whose chordal distance is L1 and whose
radius originates at the part centre.
Key
1 pulley outside diameter
NOTE The true profile of the groove sides can only be produced by plotting the function associated with the
cross-section.
Figure 5 — Groove profile — Tolerance bands — Millimetres
6.2.4 Pulley outside diameters
Pulleys outside diameters for the standard pulleys are given in Table 7. The relationship of the pulley
outside and pitch diameters is illustrated in Figure 6 and Formulae (3) and (4).
No. of grooves×pulleyp itch
Pitchd iameter= (3)
π
Outside diameter = Pitch diameter − 2a (4)
where a is given in Table 1.
Key
1 pitch 4 pitch diameter
2 belt pitch line 5 outside diameter
3 belt tooth 6 pulley groove
Figure 6 — Pulley dimensions
10 © ISO 2014 – All rights reserved

Table 7 — Standard pulley sizes
Dimensions in millimetres
Profile
Number G8M G14M
of grooves
Pitch di- Outside Pitch di- Outside
ameter diameter ameter diameter
22 56,02 54,42
25 63,66 62,06
28 71,30 69,70 124,78 121,98
29  129,23 126,43
30 76,39 74,79 133,69 130,89
31 138,15 135,35
32 81,49 79,89 142,60 139,80
33 147,06 144,26
34 86,58 84,98 151,52 148,72
35 155,97 153,17
36 91,67 90,07 160,43 157,63
37 164,88 162,08
38 96,77 95,17 169,34 166,54
39 173,80 171,00
40 101,86 100,26 178,25 175,45
42 106,95 105,35
43 191,62 188,82
44 196,08 193,28
45 114,59 112,99 200,54 197,74
48 122,23 120,63 213,90 211,10
50 127,32 125,72 222,82 220,02
53 134,96 133,36 236,19 233,39
56 142,60 141,00 249,55 246,75
152,79 151,19 267,38 264,58
63 160,43 158,83 280,75 277,95
64 162,97 161,37 285,21 282,41
67 170,61 169,01 298,57 295,77
71 180,80 179,20 316,40 313,60
72 320,86 318,06
75 190,99 189,39 334,23 331,43
80 203,72 202,12 356,51 353,71
90 229,18 227,58 401,07 398,27
112 285,21 283,61 499,11 496,31
140 356,51 354,91 623,89 621,09
168 748,66 745,86
192 488,92 487,32
180 458,37 456,77 802,14 799,34
192 855,62 852,82
200 891,27 888,47
224 570,41 568,81 998,22 995,42
6.2.5 Pulley width
The standard nominal pulley width, and the minimum actual pulley width required, b for flanged
f
pulleys, b’ for unflanged pulleys are given in Table 8 and shown in Figure 7. Users are advised that the
f
values given for b’ apply also to pulleys with only one flange (see Annex D).
f
Table 8 — Standard pulley widths
Dimensions in millimetres
Minimum pulley width
Standard nominal
Profile
pulley width
Unflanged b’
Flanged b
f f
12 14 22
21 23 30
G8M
36 40 47
62 66 74
20 26 35
37 44 52
G14M 68 76 85
90 99 107
125 134 143
The minimum unflanged pulley width can be reduced when the alignment of the drive can be controlled,
but shall not be less than the minimum flanged pulley width.
b
b
f
f
1 2
Key
1 flanged pulley
2 unflanged pulley
Figure 7 — Minimum pulley width
12 © ISO 2014 – All rights reserved

7 Profile system H
7.1 Belt dimensions and tolerances
7.1.1 Belt tooth dimensions
The nominal belt tooth dimensions are the same for single-sided and double-sided belts; they are given
in Table 9 and shown in Figure 8.
Table 9 — Nominal tooth dimensions
Dimensions in millimetres
P P P P P P P P
1 5 2 6 3 7 4 8
a
Profile Pitch h h h r r a
s d t 1 2
(X, Y) (X, Y) (X, Y) (X, Y) (X, Y (X, Y) (X, Y) (X, Y
) )
−1,14 −0,83 −0,83 0,00
H3M 3 2,4 — 1,21 — 0,30 — — 0,86 — 0,381
0,00 −0,30 −0,35 −1,21
−1,14 −0,83 −0,83 0,00
DH3M 3 — 3,2 — — 0,30 — — 0,86 — 0,381
0,76 1,06 1,11 1,97
−1,85 −1,44 −1,44 0,00
H5M 5 3,8 — 2,08 — 0,41 — — 1,50 — 0,572
0,00 −0,42 −0,53 −2,08
−1,85 −1,44 −1,44 0,00
DH5M 5 — 5,3 — — 0,41 — — 1,50 — 0,572
1,14 1,56 1,67 3,22
−3,30 −2,55 −2,47 0,00
H8M 8 6,0 — 3,38 — 0,76 — — 2,59 — 0,686
0,00 −0,65 −1,17 −3,38
−3,30 −2,55 −2,47 0,00
DH8M 8 — 8,1 — — 0,76 — — 2,59 — 0,686
1,37 2,02 2,54 4,75
−5,78 −4,36 −4,30 0,00
H14M 14 10,0 — 6,02 — 1,42 — — 4,46 — 1,397
0,00 −1,29 −1,97 −6,02
−5,78 −4,36 −4,30 0,00
DH14M 14 — 14,8 — — 1,42 — — 4,46 — 1,397
2,79 4,08 4,76 8,81
−8,34 −6,32 −6,22 0,00
H20M 20 13,2 — 8,68 — 2,03 — — 6,40 — 2,159
0,00 −1,84 −2,90 −8,68
a
a is the belt design pitch differential.
P8
X
r
a r
P7
X
X
P6
P5
X
(0,0)
a
X
P1
h
P2
h d
X
s
r a
X
P3
(0,0)
h r
t 2 X
P1
P2
X
X
X h P3 r
t r
P4
X
P4
Key
1 single-sided
2 double-sided
Figure 8 — Tooth dimensions – Profile system H
7.1.2 Belt widths and tolerances
Belt widths and tolerances are given in Table 10.
Table 10 — Widths and width tolerances
Dimensions in millimetres
Tolerance on width for belt pitch lengths
Over 840 mm and
Profile Nominal belt width
Up to and includ- Over
up to and including
ing 840 mm 1 680 mm
1 680 mm
+0,4 +0,4
—
H3M,
−0,8 −0,8
DH3M
+0,8 +0,8 +0,8
−0,8 −1,2 −1,2
+0,4 +0,4
9 —
−0,8 −0,8
H5M,
+0,8 +0,8 +0,8
DH5M
−0,8 −1,2 −1,2
+0,8 +0,8 +0,8
−0,8 −1,2 −1,2
H8M,
+0,8 +1,2 +1,2
DH8M −1,2 −1,2 −1,6
+1,6 +1,6 +2,0
−1,6 −2,0 −2,0
14 © ISO 2014 – All rights reserved

Table 10 (continued)
Tolerance on width for belt pitch lengths
Over 840 mm and
Profile Nominal belt width
Up to and includ- Over
up to and including
ing 840 mm 1 680 mm
1 680 mm
+0,8 +1,2 +1,2
−1,2 −1,2 −1,6
+1,2 +1,2 +1,6
−1,2 −1,6 −1,6
H14M,
+1,6 +1,6 +2,0
DH14M
−1,6 −2,0 −2,0
+2,4 +2,4 +2,4
−2,4 −2,8 −3,2
+2,4 +2,4 +2,4
−2,4 −2,8 −3,2
H20M
+4,8
290 — —
−6,4
7.1.3 Pitch length measurement
See Annex A for tolerances and Annex B for the relationship between the centre distance and the belt
pitch length.
7.1.3.1 Measuring fixture (see Figure 9)
The pitch length of a synchronous belt shall be determined by placing the belt on a measuring fixture
composed of the following elements.
7.1.3.2 Two pulleys of equal diameter, as specified in Table 11, of the proper belt type and having
standard tooth space dimensions. These pulleys should be made to the tolerances shown in Table 11.
One pulley shall be free to rotate on a fixed-position shaft, while the other shall be free to rotate on a
moveable shaft to permit the centre distance to change.
7.1.3.3 Means of applying a total measuring force to the moveable pulley.
7.1.3.4 Means of measuring the centre distance between the two pulleys with the necessary degree
of accuracy for centre distance measurement.
7.1.3.5 Total measuring force
The total measuring force to be applied for measuring belts is given in Table 12.
7.1.4 Procedure
In measuring the pitch length of a synchronous belt, the belt should be rotated at least two revolutions
to seat it properly and to divide the total force equally between the two spans of the belt. The pitch
length shall be calculated by adding the pitch circumference of one of the pulleys to twice the measured
centre distance.
Check double-sided belts on both tooth faces.
Key
1 centre distance
2 total measuring force
Figure 9 — Diagram of fixture for measuring pitch length
Table 11 — Belt length measuring pulleys
Dimensions in millimetres
Radial Axial
Number of Pitch Outside
runout runout
Profile
a
grooves circumference diameter
b b
F.I.M. F.I.M.
27,886
H3M, DH3M 30 90 0,013 0,025
±0,013
30,687
H5M, DH5M 20 100 0,013 0,025
±0,013
85,208
H8M, DH8M 34 272 0,013 0,025
±0,013
175,46
H14M, DH14M 40 560 0,013 0,051
±0,025
250,33
H20M 40 800 0,013 0,076
±0,036
a
Pulleys outside of the diameter tolerance range specified can be used if the resulting belt length
measurements are corrected for the actual pulley diameters.
b
Full indicator movement.
NOTE The number of pulley teeth specified in Table 11 determines the recommended sizes for measuring
the belt pitch length. Practically, other sizes of pulleys could be used provided they have the same number of
teeth, and meet the dimensional requirements of Table 11.
16 © ISO 2014 – All rights reserved

Table 12 — Total measuring force
Forces in newtons
Belt width
mm
Profile
6 9 15 20 25 30 40 50 55 85 115 170 230 290 340
H3M,
45 76 138 — — — — — — — — — — — —
DH3M
H5M,
— 111 214 — 376 — — — — — — — — — —
DH5M
H8M,
— — — 470 750 — 1 320 — 2 310 — — — — —
DH8M
H14M,
— — — — — — 1 350 — 2 130 3 660 5 180 7 960 — — —
DH14M
H20M — — — — — — — — — — 6 961 10 729 14 839 18 949 22 374
7.2 Pulleys, profile system H
7.2.1 General
See Annex C for tolerances.
The pulley is characterized by a curvilinear groove profile. This groove profile is defined as the profile
formed by the generating tool rack form required to machine-finish the curvilinear profile. The profile
is different for each pulley diameter, but can be closely approximated by a nominal groove profile over
specified ranges of number of grooves.
7.2.2 Generating tool rack
Dimensions and tolerances for the generating tool rack for pulleys with profile system H are given in
Table 13 and shown in Figure 10.
P
b
(0,0) P0
x
x r1
P1
x r2
P2
r3
h
xP3
r
r4
x
r5
P4
x
P5
X
Figure 10 — Pulley generating tool rack form

18 © ISO 2014 – All rights reserved
Table 13 — Pulley generating tool rack dimensions
Profile Number of P h Po r P r P r P r P r P X
b r 1 1 2 2 3 3 4 4 5 5
grooves
±0,012 ±0,015 (X, Y) ±0,012 (X, Y) ±0,012 (X, Y) ±0,012 (X, Y) ±0,012 (X, Y) ±0,012 (X, Y)
9 to 13 3,000 1,196 1,423 0,414 1,061 — — ∞ 0,712 0,559 0,574 0,869 0,029 0,029
0 −0,213 −0,840 −1,004 −1,196
14 to 25 3,000 1,173 1,324 0,254 1,139 0,792 0,992 ∞ 0,747 0,254 0,687 0,844 0,114 0,114
0 −0,080 −0,213 −0,860 −0,944 −1,168
H3M
26 to 80 3,000 1,227 1,223 0,262 0,982 2,616 0,820 — — 0,493 0,733 0,869 0,036 0,036
0 −0,159 −0,679 -0,877 -1,227
81 to 200 3,000 1,232 1,333 0,358 0,981 — — ∞ 0,923 — — 0,866 0,077 0,077
0 −0,290 −0,554 -1,232
12 to 16 5,000 1,986 2,344 0,659 1,739 4,475 1,522 ∞ 1,124 0,691 0,773 1,133 0,328 0,328
0 −0,316 −0,720 −1,560 −1,895 −1,986
17 to 31 5,000 2,024 2,242 0,610 1,871 1,431 1,540 ∞ 1,163 0,612 1,013 1,219 0,295 0,295
0 −0,126 −0,593 −1,566 −1,789 −2,024
H5M
32 to 79 5,000 2,032 2,073 0,493 1,675 1,359 1,501 ∞ 1,370 1,402 1,088 1,300 0,135 0,135
0 −0,203 −0,566 −1,035 −1,617 −2,032
80 to 200 5,000 2,056 2,160 0,610 1,564 — — ∞ 1,443 — — 1,471 0,043 0,043
0 −0,483 −1,050 −2,065
22 to 27 8,000 3,289 3,805 1,143 2,738 — — ∞ 2,322 — — 2,553 0 —
0 −0,648 −1,801 −3,289
28 to 89 8,000 3,612 3,754 1,067 2,748 12,903 2,360 — — 0,726 2,283 2,744 0 —
H8M
0 −0,711 −2,024 −2,215 −3,612
90 to 200 8,000 3,632 3,617 0,940 2,697 — — ∞ 2,459 — — 2,637 0 —
0 −0,757 −1,948 −3,632
28 to 36 14,000 6,320 6,761 1,880 5,037 20,828 4,064 — — 1,143 3,909 4,717 0 —
0 −1,133 −3,904 −4,242 −6,320
37 to 89 14,000 6,223 6,599 1,829 4,890 15,748 4,204 — — 1,143 4,089 4,663 0 —
H14M
0 −1,176 −3,493 −3,802 −6,223
90 to 216 14,000 6,350 6,546 1,905 4,704 20,117 4,288 — — 0,254 4,270 4,623 0 —
0 −1,425 −3,439 −3,498 −6,350
34 to 45 20,000 8,644 9,786 2,814 7,105 — — ∞ 5,972 — — 5,625 0,753 0,753
0 −1,852 −4,947 −8,644
46 to 100 20,000 8,591 9,529 2,667 7,041 20,329 6,015 — — — — 5,842 0,711 0,711
H20M
0 −1,662 −5,121 −8,591
101 to 220 20,000 8,690 9,787 2,676 7,305 — — ∞ 6,165 — — 5,733 0,739 0,739
0 −1,760 −4,855 −8,690
7.2.3 Pulley groove profile dimensions and tolerances
Dimensions and tolerances for the pulley grooves with profile H are given in Table 14 and shown in
Figure 11.
Table 14 — Pulley groove profile dimensions
Dimensions in millimetres
Number of Profile
Profile H X R ϕ° R
g 1 2
a
grooves band
10 to 13 1,190 0,029 0,991 15 0,181
14 to 25 1,179 0,112 0,889 9 0,229
H3M ±0,051
26 to 80 1,219 0,028 0,927 8 0,191
81 to 200 1,234 0,074 0,925 4 0,301
12 to 16 1,989 0,307 1,265 10 0,432
17 to 25 2,009 0,320 1,270 6 0,508
H5M ±0,051
26 to 80 2,052 0,081 1,438 2 0,488
81 to 200 2,056 0,028 1,552 5 0,569
22 to 27 3,295 0,000 2,675 11,3 0,874
+0,090
H8M 28 to 89 3,604 0,000 2,629 7 1,024
−0,080
90 to 200 3,630 0,000 2,639 6,6 1,008
28 to 32 6,327 0,000 4,859 7,1 1,544
33 to 36 6,328 0,000 4,834 5,2 1,613
+0,090
37 to 57 6,198 0,000 4,737 9,3 1,654
H14M
58 to 89 6,198 0,000 4,669 8,9 1,902
−0,080
90 to 153 6,328 0,000 4,636 6,9 1,704
154 to 216 6,327 0,000 4,597 8,6 1,770
32 to 45 8,649 0,544 6,185 15 2,184
H20M 46 to 100 8,661 0,544 6,185 10 2,540 ±0,089
101 to 220 8,700 0,544 6,185 18 2,540
a
The profile band tolerance through R2 blends into the pulley OD tolerance so that the pulley OD and profile band
tolerances do not conflict.
R2
R
H
g
X
o
Key
1 minimum
2 maximum
3 pulley outside diameter
Figure 11 — Pulley groove profile and tolerance bands
20 © ISO 2014 – All rights reserved

7.2.4 Pulley outside diameters
Pulley outside diameters for the standard pulleys are given in Table 15. The relationship of the pulley
outside and pitch diameters is illustrated in Figure 12 and Formulae (5) and (6).
No. of grooves×pulleyp itch
Pitchd iameter= (5)
π
Outside diameter = Pitch diameter − 2a + N’ (6)
where
a is given in Table 9;
N’ is given in Table 16.
Key
1 pitch
2 belt pitch line
3 belt tooth
4 pitch diameter
5 outside diameter
6 pulley groove
Figure 12 — Pulley dimensions
Table 15 — Standard pulley sizes
Dimensions in millimetres
Profile
Num-
H3M H5M H8M H14M H20M
ber of
Pitch Outside Pitch Outside Pitch Outside Pitch Outside Pitch Outside
grooves
diameter diameter diameter diameter diameter diameter diameter diameter diameter diameter
14 13,37 12,61 22,28 21,14 — — — — — —
15 14,32 13,56 23,87 22,73 — — — — — —
16 15,28 14,52 25,46 24,32 — — — — — —
17 16,23 15,47 27,06 25,91 — — — — — —
18 17,19 16,43 28,65 27,50 — — — — — —
19 18,14 17,38 30,24 29,10 — — — — — —
20 19,10 18,34 31,83 30,69 — — — — — —
21 20,05 19,29 33,42 32,28 — — — — — —
22 21,01 20,25 35,01 33,87 56,02 54,65 — — — —
24 22,92 22,16 38,20 37,05 61,12 59,74 — — — —
25 — — — — 63,66 62,29 — — — —
26 24,83
24,07 41,38 40,24 66,21 64,84 — — — —
28 26,74 25,98 44,56 43,42 71,30 70,08 124,78 122,12 — —
29 — — — — —
— 129,23 126,57 — —
30 28,65 27,89 47,75 46,60 76,39 75,13 133,69 130,99 — —
32 30,56 29,80 50,93 49,79 81,49 80,16 142,60 139,88 — —
34 32,47 31,71 54,11 52,97 86,58 85,21 151,52 148,79 216,45
212,13
36 34,38 33,62 57,30 56,15 91,67 90,30 160,43 157,68 229,18 224,87
38 36,29 35,53 60,48 59,34 96,77 95,39 169,34 166,60 241,92 237,60
40 38,20 37,44 63,66 62,52 101,86 100,49 178,25 175,49 254,65 250,33
43 41,06 40,30 68,44 67,29 — — — — — —
44 42,02 41,25 70,03 68,89 112,05 110,67 196,08 193,28 280,11 275,79
46 43,93 43,16 73,21 72,07 — — — — — —
48 45,48 45,07 76,39 75,25 122,23 120,86 213,90 211,11 305,58 301,26
49 46,79 46,03 77,99 76,84 — — — — — —
50 47,75 46,98 79,58 78,43 — — — — — —
52 49,66 48,89 82,76 81,62 — — 231,73 228,94 331,04 326,72
55 52,52 51,76 87,54 86,39 — — — — — —
56 — — 89,13 87,98 142,60 141,23 249,55 246,76 356,51 325,19
60 57,30 56,53 95,49 94,35 — — 267,38 264,59 381,97 377,65
62 —
— 98,68 97,53 — — — — — —
22 © ISO 2014 – All rights reserved

Table 15 (continued)
Profile
Num-
H3M H5M H8M H14M H20M
ber of
Pitch Outside Pitch Outside Pitch Outside Pitch Outside Pitch Outside
grooves
diameter diameter diameter diameter diameter diameter diameter diameter diameter diameter
64 — — — — 162,97 161,60 285,21 282,41 407,44 403,12
65 62,07 61,31 103,45 102,31 —
— — — — —
68 — — — — — — 303,03 300,24 432,90 428,58
70 66,85 66,08 111,41 110,27 — — —
— — —
72 68,75 67,99 — — 183,35 181,97 320,86 318,06 458,37 454,05
75 71,62 70,86 119,37 118,22 — — — — —
—
78 74,48 73,72 124,14 123,00 — — — — — —
80 76,39 75,63 127,32 126,18 203,72 202,35 356,51 353,71 509,30 504,98
90 85,94 85,18 143,24 142,10 229,18 227,81 401,07 398,28 572,96 568,64
100 95,49 94,73 159,15 158,01 — — — — — —
110 105,04 104,28 175,07 173,93 — — — — — —
112 — — — — 285,21 283,83 499,11 496,32 713,01 708,70
120 114,59 113,83 190,99 189,84 — — — — — —
130 124,14 123,38 206,90 205,76 — — — — — —
140 133,69 132,92 222,82 221,67 — — — — — —
144 — — — — 366,69 365,32 641,71 638,92 916,73 912,41
150 143,24 142,48 238,73 237,59 — — — — — —
160 152,79 152,03 254,65 235,50 — — — — — —
168 — — — — 427,81 426,44 748,66 745,87 1 069,52 1 065,20
192 — — — 488,92 487,55 855,62 852,82 1 222,31 1 217,99
—
216 — — — — — 962,57 959,78 1 375,10 1 370,78
Table 16 — Values of chordal correction factor N’
Dimensions in millimetres
Profile
Number of grooves H8M H14M
Value of N’ Value of N’
28 0,15 0,15
29 0,15 0,13
30 0,10 0,09
31 0,08 0,09
32 0,05 0,08
33 0,03 0,08
34 0,08
35 0,05
36 0,05
37 0,05
38 0,05
39 0,03
40 0,03
NOTE N’ values for H3M, H5M, and H20M are zero.
7.2.5 Pulley width
The standard nominal pulley width and the minimum actual pulley width required, b for flanged
f
pulleys, b’ for unflanged pulleys are given in Table 17and shown in Figure 6. Users are advised that the
f
values given for b’ apply also to pulleys with only one flange (see Annex D).
f
Table 17 — Standard pulley widths
Dimensions in millimetres
Minimum pulley width
Standard nominal
Profile
pulley width
Unflanged b’
Flanged b
f f
6 8 11
H3M 9 11 14
15 17 20
9 11 15
H5M 15 17 21
25 27 31
20 22 30
30 32 40
H8M
50 53 60
85 89 96
40 42 55
55 58 70
H14M 85 89 101
115 120 131
170 175 186
115 120 134
170 175 189
H20M 230 235 251
290 300 311
340 350 361
NOTE The minimum unflanged pulley width can be reduced when the alignment of the drive can be controlled but shall
not be less than the minimum flanged pulley width.
b
b
f
f
1 2
Key
1 flanged pulley
2 unflanged pulley
Figure 13 — Minimum pulley width
24 © ISO 2014 – All rights reserved

8 Profile system R
8.1 Belt dimensions and
...