ISO 17396:2017

Synchronous belt drives - Metric pitch - Tooth profiles T and AT endless and open ended belts and pulleys

ISO 17396:2017 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, 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, and 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 belt. 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.

Transmissions synchrones par courroies — Pas métrique — Poulies et courroies dentées sans fin ou à bout libre à dents de profil T ou AT

General Information

• Status: Published
• Publication Date: 23-Nov-2017
• ICS: 21.220.10 - Belt drives and their components
• Technical Committee: ISO/TC 41/SC 4 - Synchronous belt drives
• Drafting Committee: ISO/TC 41/SC 4 - Synchronous belt drives
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 04-Sep-2024
• Completion Date: 13-Dec-2025

Relations

• Revised: ISO 17396:2024 - Synchronous belt drives - Metric pitch - Tooth profiles T and AT endless and open ended belts and pulleys
• Effective Date: 09-Dec-2023
• Revises: ISO 17396:2014 - Synchronous belt drives - Metric pitch, trapezoidal profile systems T and AT, belts and pulleys
• Effective Date: 23-Jan-2016

Overview

ISO 17396:2017 – Synchronous belt drives - Metric pitch - Tooth profiles T and AT defines the principal characteristics of metric synchronous (timing) belts and pulleys for profile systems T and AT. It covers both endless and open-ended belts used for mechanical power transmission and positive indexing/synchronization. The standard clarifies belt and pulley nomenclature, dimensions, tolerances, measurement procedures and material considerations for reliable design, manufacture and verification.

Key topics and technical requirements

• Profile families and pitches: Standardizes eight profiles - T2.5, T5, T10, T20 and AT3, AT5, AT10, AT20 - with their nominal tooth geometries and pitch values.
• Tooth geometry and tolerances: Specifies nominal tooth dimensions (head, root, angles and radii) for single- and double-sided belts and matching pulley groove profiles.
• Belt widths and tolerances: Lists standard nominal widths and manufacturing tolerances for each profile system.
• Pitch length measurement: Defines two measurement methods - using two matched pulleys (for molded endless belts) or toothed clamps (for very long/open belts) - and specifies measuring fixtures, centre-distance measurement and total measuring forces.
• Pulley dimensions and quality: Details groove dimensions, pulley diameters, widths, tolerances and quality/finish requirements for pulleys that mate with T and AT belts. (See normative tables in the standard.)
• Materials and cord types: Notes that T/AT belts are typically polyurethane with high-tension fine steel cords; values given in the document apply to these materials. Alternate tensile cords (aramid, glass-fibre reinforced rubber, etc.) may affect performance and should be agreed upon between user and manufacturer.
• Spliced/open belts: Allows splicing thermoplastic polyurethane open belts into endless belts for conveyors, but excludes splice-region tolerances from the standard limits.
• Nomenclature rules: Establishes designation formats for belts (width-profile-pitch-length) and pulleys (P + grooves + profile + pitch + width).

Applications

ISO 17396:2017 is intended for:

• Power transmission systems requiring precise speed ratio and indexing (printer feeds, robotics, packaging, cam drives).
• Conveyor systems using spliced thermoplastic belts.
• Design, specification and quality control of timing belt drives in industrial machinery and automotive ancillary systems.

Who uses this standard

• Mechanical design and power transmission engineers
• Belt and pulley manufacturers and toolmakers
• Quality assurance and metrology teams (inspection labs)
• Procurement specialists and OEMs specifying component interchangeability
• Maintenance and service teams verifying replacements

Related standards

• ISO 254 (Belt drives - Pulleys - Quality, finish and balance) is referenced for pulley quality and finish requirements.

ISO 17396:2017 ensures compatibility, interchangeability and predictable performance of metric synchronous belts and pulleys (T and AT), helping engineers and manufacturers design and verify reliable timing-belt drive systems.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 17396
Second edition
2017-11
Synchronous belt drives — Metric 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 2017
© ISO 2017, 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. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Belt profile systems . 2
5 Belt nomenclature . 2
6 Pulley profile systems . 2
7 Pulley nomenclature . 3
8 Belt profile systems T and AT . 4
8.1 Belt profile systems T and AT — General . 4
8.2 Profile system T — Belt tooth dimensions and tolerances . 4
8.3 Profile system AT — Belt tooth dimensions and tolerances . 5
9 Belt widths and tolerances. 5
10 Pitch length measurement . 6
10.1 Endless belts manufactured in circular moulds . 6
10.2 For very long endless belts and open belts . 7
10.3 Total measuring forces . 7
10.4 Procedures . 8
10.4.1 For endless belts manufactured in circular moulds . 8
10.4.2 For very long endless belts and open belts . 8
10.5 Belt length tolerances . 8
11 Pulleys .10
11.1 General profile system T .10
11.1.1 General.10
11.1.2 Profile system T — Pulley groove dimensions and tolerances .10
11.1.3 Profile system T — Pulley groove profile .11
11.1.4 Profile system T — Pulley diameters .11
11.1.5 Profile system T — Pulley width .12
11.2 General profile system AT.13
11.2.1 General.13
11.2.2 Profile system AT — Pulley groove profile dimensions and tolerances .13
11.2.3 Profile system AT — Pulley groove profile .14
11.2.4 Profile system AT — Pulley diameters .14
11.2.5 Pulley system AT — Pulley width.14
Annex A (normative) Pulley tolerances .16
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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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
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on the ISO list of patent declarations received (see www.iso.org/patents).
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For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
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World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 41, Pulleys and belts (including veebelts),
Subcommittee SC 4, Synchronous belt drives.
This second edition cancels and replaces the first edition (ISO 17396:2014), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— root diameter specifications for AT series pulleys (Figure 6 and Table 12) have been added.
iv © ISO 2017 – All rights reserved

INTERNATIONAL STANDARD ISO 17396:2017(E)
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, 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, and
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 belt. 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 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 http://www.electropedia.org/
4 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
5 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
G T G
tooth 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 length; for spliced belts, use the
letter “V.”
EXAMPLE 1 A metric synchronous belt of 10 mm pitch, profile system T, 50 mm wide, and 1 400 mm in pitch
length is designated as follows:
— for a single-sided belt: 50 - T10 - 1 400;
— for a double-sided belt: 50 - D - T10 - 1 400 or 50 - D - T10 - 1 400.
G T
EXAMPLE 2 A metric synchronous belt of 5 mm pitch, profile system AT, 25 mm wide, and 500 mm in pitch
length (number of teeth = 100) is designated as follows:
— for a single-sided belt: 25 - AT5 - 500 (100 t);
— for double-sided belt: 25 - D - AT5 - 500 (100 t) or 25 - D - AT5 - 500 (100 t).
G T
EXAMPLE 3 An open metric synchronous belt of 5 mm pitch, profile system AT, 25 mm wide, and 50 000 mm
in pitch length is designated as
25 - AT5 - 50 000 - M.
6 Pulley profile systems
Eight pulley profiles for synchronous drives are standardized.
2 © ISO 2017 – All rights reserved

Profile system T: Profile system AT:
—  profile T2,5 —  profile AT3
—  profile T5 —  profile AT5
—  profile T10 —  profile AT10
—  profile T20 —  profile AT20
7 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 designated, as is the belt, by a combination of numbers and letters as follows:
a) the letter “P”, which indicates a pulley;
b) the number of grooves;
c) the profile system;
d) the groove pitch, in millimetres;
e) the width, in millimetres.
EXAMPLE A pulley for a metric toothed belt which has 20 mm pitch and 30 grooves with a nominal width of
50 mm is identified as follows:
— for T-profile system pulley: P30 - T20 - 50;
— for AT-profile system pulley: P30 - AT20 - 50.
8 Belt profile systems T and AT
8.1 Belt profile systems T and AT — General
Key
1 single-sided metric synchronous belt
2 symmetrical double-sided metric synchronous belt
3 asymmetric double sided metric synchronous belt
Figure 1 — Belt dimensions for profile systems T and AT
8.2 Profile system T — Belt tooth dimensions and tolerances
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.
4 © ISO 2017 – All rights reserved

Table 1 — Profile system T — Nominal tooth dimensions
Belt Pitch Tooth Root width
profile angle
P 2β S h h h r min. r ± 0,1
b r s d t a r
mm degrees mm mm mm mm mm mm
T2,5 2,5 40 ± 2 1,50 ± 0,05 1,30 ± 0,15 1,90 0,70 ± 0,05 0,2 0,2
T5 5,0 40 ± 2 2,65 ± 0,05 2,20 ± 0,15 3,25 1,20 ± 0,05 0,4 0,4
T10 10,0 40 ± 2 5,30 ± 0,10 4,50 ± 0,30 6,80 2,50 ± 0,10 0,6 0,6
T20 20,0 40 ± 2 10,15 ± 0,15 8,00 ± 0,45 12,85 5,00 ± 0,15 0,8 0,8
NOTE  The value of h can vary due to process-related adjustments of the manufacturer.
d
8.3 Profile system AT — Belt tooth dimensions and tolerances
The nominal belt tooth dimensions are the same for single-sided and double-sided belts; they are given
in Table 2 and shown in Figure 1.
Table 2 — Profile system AT — Nominal tooth dimensions
Belt Tooth
Pitch Head width
profile angle
P 2β S h h h r min. r ± 0,1
b h s d t a r
mm degrees mm mm mm mm mm mm
a
AT3 3,0 50 ± 2 1,50 ± 0,05 1,90 ± 0,15 n.a. 1,10 ± 0,05 0,3 0,1
a
AT5 5,0 50 ± 2 2,50 ± 0,05 2,70 ± 0,15 3,05 1,20 ± 0,05 0,4 0,6
a
4,50 ± 0,30
AT10 10,0 50 ± 2 5,00 ± 0,10 6,50 2,50 ± 0,10 0,6 1,2
(5,0)
a
8,00 ± 0,45
AT20 20,0 50 ± 2 10,00 ± 0,15 12,15 5,00 ± 0,15 1,6 2,5
(9,0)
NOTE  The value of h can vary due to process-related adjustments of the manufacturer.
d
a
The thickness of the backside depends on the method of manufacturing.
9 Belt widths and tolerances
Belt widths and tolerances are given in Table 3.
Table 3 — Belt widths and width tolerances
Dimensions in millimetres
Belt profile Nominal belt width Tolerance
T2,5 — 4 6 10 ±0,3
T5 6 10 16 25 ±0,5
T10 16 25 32 50 ±0,5
T20 32 50 75 100 ±1,0
AT3 6 10 16 25 ±0,3
AT5 6 10 16 25 ±0,5
AT10 16 25 32 50 ±0,5
AT20 32 50 75 100 ±1,0
NOTE  Tolerances for larger belt widths and closer tolerances to be confirmed between the user and the manufacturer.
10 Pitch length measurement
10.1 Endless belts manufactured in circular moulds
10.1.1 The pitch length of a synchronous belt shall be determined by placing the belt on a measuring
fixture (see Figure 2) composed of the elements given in 10.1.2 to 10.1.4.
10.1.2 Two pulleys of equal diameter, as specified in Table 4, of the proper profile shown in Table 7.
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.
10.1.3 Means of applying a total measuring force to the moveable pulley, as given in Table 5.
10.1.4 Means of measuring the centre distance between the two pulleys with the necessary degree of
accuracy f
...