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INTERNATIONAL ISO
STANDARD 13050

First edition
1999-12-15

Curvilinear toothed synchronous belt drive

systems
Transmissions par courroies synchrones à denture curviligne

Reference number
ISO 13050:1999(E)

© ISO 1999
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ISO 13050:1999(E)

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ISO 13050:1999(E)

Contents Page

Foreword.....................................................................................................................................................................iv
Introduction .................................................................................................................................................................v
1 Scope ..............................................................................................................................................................1
2 Normative reference ......................................................................................................................................1
3 Belt types........................................................................................................................................................1
4 Belt nomenclature..........................................................................................................................................2
5 Pulley types ....................................................................................................................................................2
6 Pulley nomenclature......................................................................................................................................2
7 Type H system................................................................................................................................................3
8 Type R system..............................................................................................................................................13
9 Type S system..............................................................................................................................................22
Annex A (normative) Belt pitch lengths and tolerances .......................................................................................31
Annex B (normative) Relationship between centre distance and belt pitch length...........................................32
Annex C (normative) Pulley tolerances ..................................................................................................................34
Annex D (informative) Flange dimensions..............................................................................................................37

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ISO 13050:1999(E)

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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.

Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.

International Standard ISO 13050 was prepared by Technical Committee ISO/TC 41, Pulleys and belts (including
veebelts), Subcommittee SC 4, Synchronous belt drives.

Annexes A , B and C form a normative part of this International Standard. Annex D is for information only.

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ISO 13050:1999(E)

Introduction
The International Organization for Standardization (ISO) draws attention to the fact that it is claimed that
compliance with this International Standard may involve the use of a patent concerning belt tooth and pulley groove
profiles given in 8.1.1 and 8.2.2.

ISO takes no position concerning the evidence, validity and scope of this patent right.

The holder of this patent right has assured ISO that he is willing to negotiate licences under reasonable and non-
discriminatory terms and conditions with applicants throughout the world. In this respect, the statement of the
holder of this patent right is registered with ISO. Information may be obtained from:

Dayco Products, Inc.

1 Prestige Place
P.O. Box 1004
Dayton, OH 45401-1004
USA

Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights other than those identified above. ISO shall not be held responsible for identifying any or all such
patent rights.

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INTERNATIONAL STANDARD ISO 13050:1999(E)

Curvilinear toothed synchronous belt drive systems

1 Scope
This International Standard specifies the principal characteristics of synchronous endless belts and pulleys for use
in synchronous belt drives1) for mechanical power transmission and where positive indexing or synchronization
may be required.

The principal belt and pulley characteristics include:

a) nominal belt tooth dimensions;

b) belt tooth pitch spacing;

c) belt length and width dimensions;

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 reference
The following normative document contains provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent edition of the normative document indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.

ISO 254:1998, Belt drives — Pulleys — Quality, finish and balance.

3 Belt types
Six belt types for synchronous drives are standardized:

¾ type H8M (H-type tooth profile);

¾ type S8M (S-type tooth profile);

¾ type R8M (R-type tooth profile);

1) Synchronous belt drives have been known by various titles in the past: for example, timing belt drives, positive belt drives,
gear belt drives.

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ISO 13050:1999(E)

¾ type H14M (H-type tooth profile);

¾ type S14M (S-type tooth profile);

¾ type R14M (R-type tooth profile).

4 Belt nomenclature
A belt is identified by a combination of numbers and letters as follows:

a) the belt pitch length in millimetres;

b) the type of tooth profile;

c) the tooth pitch in millimetres;

d) the width in millimetres or 10 times the width in millimetres for the S-type belt;

e) double-sided belts are designated by adding the letter "D" before the tooth profile letter.

EXAMPLE A curvilinear tooth synchronous belt of 14 mm pitch, 40 mm wide, 1 400 mm in pitch length is identified as
follows:

1400-H14M-40 for H-type single-sided belt, 1400-DH14M-40 for H-type double-sided belt;

400-S14M-1400 for S-type single-sided belt, 400-DS14M-1400 for S-type double-sided belt;

1400-R14M-40 for R-type single-sided belt, 1400-DR14M-40 for R-type double-sided belt.

5 Pulley types
Six pulley types for synchronous drives are standardized:

¾ type H8M (H-type groove profile);

¾ type S8M (S-type groove profile);

¾ type R8M (R-type groove profile);

¾ type H14M (H-type groove profile);

¾ type S14M (S-type groove profile);

¾ type R14M (R-type groove profile).

6 Pulley nomenclature
A pulley for a synchronous drive is identified by the number of grooves, the groove pitch and profile, and the width.
It is identified as is the belt by a combination of numbers and letters as follows:

a) the letter "P" indicates a pulley;

b) the number of grooves;

c) the type of groove profile;

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ISO 13050:1999(E)

d) the groove pitch in millimetres;

e) the width in millimetres or ten times the width in millimetres for S-type pulleys.

EXAMPLE A pulley for a curvilinear toothed belt which has 14 mm pitch and 30 grooves with a nominal width of 40 mm is
identified as follows:

P30-H14M-40 for H-type pulleys;

P30-S14M-0400 for S-type pulleys;

P30-R14M-40 for R-type pulleys.

7 Type H system

7.1 H-type 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 1
and shown in Figure 1.

Table 1 — Nominal tooth dimensions

Dimensions in millimetres

Belt type Pitch hs hd ht X Y rbb rr aa

ref. ref.
H8M 8 6 3,38 0,089 0,787 2,59 0,76 0,686
DH8M 8 8,1 3,38 0,089 0,787 2,59 0,76 0,686
H14M 14 10 6,02 0,152 1,470 4,55 1,35 1,397
DH14M 14 14,8 6,02 0,152 1,470 4,55 1,35 1,397
a a is the belt design pitch differential.

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ISO 13050:1999(E)

Key
1 Single-sided belts
2 Double-sided belts

Figure 1 — Belt tooth dimensions

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ISO 13050:1999(E)

7.1.2 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

Belt type Nominal belt width Over 840 mm and up

Up to and including Over
to and including
840 mm 1 680 mm
1 680 mm
20 + 0,8 + 0,8 + 0,8
30 - 0,8 - 1,3 - 1,3
H8M
+ 1,3 + 1,3 + 1,3
50
- 1,3 - 1,3 - 1,5
DH8M
+ 1,5 + 1,5 +2
85
- 1,5 - 2,0 -2

+ 0,8 + 0,8 + 1,3

40
- 1,3 - 1,3 - 1,5
H14M + 1,3 + 1,5 + 1,5
55
- 1,3 - 1,5 - 1,5

+ 1,5 + 1,5 +2
85
- 1,5 - 2,0 -2
DH14M
115 + 2,3 + 2,3 + 2,3
170 - 2,3 - 2,8 - 3,3

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 3)

The pitch length of a synchronous belt shall be determined by placing the belt on a measuring fixture composed of
the following elements.

7.1.3.1.1 Two pulleys of equal diameter, as specified in Table 3, of the proper belt type and having standard
tooth space dimensions. These pulleys should be made to the tolerances shown in Table 3 and have the proper
clearance Cm, between pulley and theoretical belt as specified in Table 3 (see Figure 2). One pulley shall be free to
rotate on a fixed-position shaft, while the other shall be free to rotate on a movable shaft to permit the centre
distance to change.

7.1.3.1.2 Means of applying a total measuring force to the movable pulley.

7.1.3.1.3 Means of measuring the centre distance between the two pulleys with the necessary degree of
accuracy for centre distance measurement.

NOTE The number of pulley teeth specified in Table 3 determine 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.

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