ISO 17396:2024

International
Standard
ISO 17396
Third edition
Synchronous belt drives — Metric
2024-09
pitch — Tooth profiles T and AT
endless and open ended belts
and pulleys
Transmissions synchrones par courroies — Pas métrique —
Poulies et courroies dentées sans fin ou à bout libre à dents de
profil T ou AT
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Belt profile systems . 2
6 Belt nomenclature . 2
7 Pulley profile systems . 3
8 Pulley nomenclature . . 3
9 Belt profile systems T and AT . 4
9.1 Belt profile systems T and AT — General .4
9.2 Profile system T — Belt tooth dimensions and tolerances .5
9.3 Profile system AT — Belt tooth dimensions and tolerances .5
10 Belt widths and tolerances . 6
11 Pitch length measurement . 6
11.1 Endless belts manufactured in circular moulds .6
11.2 For very long endless belts and open belts .7
11.3 Total measuring forces .8
11.4 Procedures .8
11.4.1 For endless belts manufactured in circular moulds .8
11.4.2 For very long endless belts and open belts .9
11.5 Belt length tolerances .9
12 Pulleys . 10
12.1 General profile system T .10
12.1.1 General .10
12.1.2 Profile system T — Pulley groove dimensions and tolerances . .10
12.1.3 Profile system T — Pulley groove profile .11
12.1.4 Profile system T — Pulley diameters .11
12.1.5 Profile system T — Pulley width . 12
12.2 General profile system AT . 13
12.2.1 General . 13
12.2.2 Profile system AT — Pulley groove profile dimensions and tolerances. 13
12.2.3 Profile system AT — Pulley groove profile .14
12.2.4 Profile system AT — Pulley diameters .14
12.2.5 Pulley system AT — Pulley width . 15
Annex A (normative) Pulley tolerances.16

iii
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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This document was prepared by Technical Committee ISO/TC 41, Pulleys and belts (including veebelts),
Subcommittee SC 4, Synchronous belt drives.
This third edition cancels and replaces the second edition (ISO 17396:2017), of which it constitutes a minor
revision.
The change is as follows:
— Clause 4 has been added.
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.

iv
International Standard ISO 17396:2024(en)
Synchronous belt drives — Metric pitch — Tooth profiles T
and AT endless and open ended belts and pulleys
1 Scope
This document specifies the principal characteristics of synchronous endless and open belts and pulleys
of the profile systems T and AT for use in synchronous belt drives for mechanical power transmission and
where positive indexing or synchronization can be required.
NOTE Synchronous belt drives have been known by various titles in the past, for example: timing belt drives,
positive belt drives, and gear belt drives.
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.
The belts of the profile systems T and AT are made of polyurethane with high-tension fine steel cord tension
members in most cases. As far as certain forces are given in this document, these values are only valid for
these kinds of belts. For polyurethane belts with different tensile cords, i.e. aramid or rubber belts reinforced
with glass fibre, the values can be different. It is intended that the user and the manufacturer agree about
suitable values. Open belts made of thermoplastic polyurethane can be spliced to work as endless belts in
conveyor applications. In this case, the tolerances are not valid for the splicing area of the endless spliced belt.
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 254, Belt drives — Pulleys — Quality, finish and balance
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 Symbols
Symbol Description Units
2β tooth angle
2ϕ groove angle
a pitch line differential mm
b minimum pulley width – flanged pulley mm
f
b’ minimum pulley width – unflanged pulley mm
f
b width at groove crest mm
r
b width at groove root mm
w
C centre distance mm
d pitch diameter mm
d outside diameter mm
o
d diameter at root mm
R
h height of a double-sided belt mm
d
h groove depth mm
g
h height of a single-sided belt mm
s
h tooth height mm
t
P pitch of the teeth of the belt and pulleys mm
b
r radius at tooth tip mm
a
r radius at the groove root mm
b
r radius at tooth root mm
r
r radius at the groove crest mm
t
S width at tooth head mm
h
S width at tooth root mm
r
5 Belt profile systems
Eight belt profiles for synchronous drives are standardized.
Profile system T: Profile system AT:
—  profile T2,5 —  profile AT3
—  profile T5 —  profile AT5
—  profile T10 —  profile AT10
—  profile T20 —  profile AT20
6 Belt nomenclature
A belt is designated by a combination of numbers and letters as follows:
a) the width, in millimetres;
b) the profile system;
c) the pitch, in millimetres;
d) the belt pitch length, in millimetres (and add the number of teeth in brackets, if required);

e) double-sided belts are designated by adding D or D before the profile system letter: D if the tooth
G T G
position is opposite gap; D if the tooth position is opposite tooth;
T
f) open belts are designated by adding the letter “M” behind the le
...