ISO 17396 defines the principal dimensions, tolerances, and quality requirements for metric-pitch synchronous belt drives using the T and AT trapezoidal tooth profiles, covering belt tooth geometry, pitch, length and width, pulley groove geometry, and pulley diameter and width tolerances [S1][S3].
The 2014 first edition ran 18 pages under ISO/TC 41/SC 4 and was withdrawn on 2017-11-24 in favour of ISO 17396:2017, which is also withdrawn and superseded by ISO 17396:2024 [S1][S3]. The two profile systems T and AT are grouped together in a single document so that designers do not have to mix specifications across standards for different metric pitches on the same drive.
Scope, profile families, and construction
ISO 17396 covers both endless and open (endless and open-ended) T and AT profile belts with their mating pulleys for mechanical power transmission and positive indexing or synchronization applications [S1][S3]. The standard names seven mandatory characteristic groups: nominal belt tooth dimensions, belt tooth pitch spacing, belt length and width, belt length measurement specifications, pulley groove dimensions and tolerances, pulley diameter and width dimensions and tolerances, and pulley quality specification [S1][S3].
Construction is restricted by the standard: T and AT belts are made predominantly of polyurethane with high-tension fine steel cord tension members, and the force values given in the document are valid only for that construction [S3]. Aramid-cord polyurethane belts and glass-fibre-reinforced rubber belts are explicitly flagged as construction variants where the tabulated force values may not apply, with the standard requiring user/manufacturer agreement on suitable replacement values [S3]. Open belts made of thermoplastic polyurethane can be spliced to form endless belts for conveyors, but the document states that its tolerances do not apply within the splicing area [S3].
Why the standard keeps being re-issued
The 2014 edition was published 2014-01-16 after a five-stage approval pipeline running 2009-10 to 2013-11, and was flagged for revision on 2015-12-19, with formal withdrawal on 2017-11-24 [S1]. The 2017 second edition followed a shorter three-stage track, with the committee draft registered 2016-06-03, DIS approved 2017-06-01, and publication 2017-11 [S3]. Both editions are now marked Withdrawn (stage 95.99) and are both superseded by ISO 17396:2024 [S1][S3].
Two practical takeaways for engineers: first, only the 2024 edition is the current reference for new designs, although 2017 drawings and catalogues remain common in field equipment; second, ICS 21.220.10 (TC 41/SC 4) places ISO 17396 in the same family as ISO 13050, which covers the higher-torque curvilinear (HTD) profile, and the two are routinely used together when a drive has both a power section and a timing section [S7][S8]. ISO 13050 is a separate, parallel standard that does not replace ISO 17396 [S8].
Pulley geometry, tolerances, and tooth-count limits
Section 11.1.3 of the standard lays down the T-profile pulley groove geometry, including tooth angle, depth, and flank tolerances that drive designers must respect when machining or specifying pulleys [S4]. Pulley diameter and width tolerances sit in the same mandatory characteristic list as groove geometry, so a T or AT pulley drawing must carry all three groups to be considered compliant [S1][S3].
A 2023 analytical study used ISO 17396:2017 as its reference for pulley tooth geometry when deriving the permissible range of teeth for non-involute tooth forms generated against a fixed reference profile, confirming that the standard is treated as the geometry-of-record for trapezoidal metric synchronous pulleys by current academic work [S9]. For comparison, the standard's T family covers smaller metric pitches while AT covers the larger metric pitches, and the standard's quality specification clause sets the maximum runout, tooth-to-tooth angular error, and radial/axial eccentricity bands that the pulley must stay within [S1][S3]. Designers specifying pulleys for indexing, where tooth positional accuracy drives machine repeatability, should weight the quality clause more heavily than for pure power transmission.
Selection criteria and how T and AT compare
T-profile metric pitches and AT-profile metric pitches are not interchangeable: the two systems are written into the same document precisely so that a designer can pull both off one shelf, but each profile is keyed to a specific metric pitch family and load class [S1][S3][S8]. In practice, T is selected for lighter-duty timing applications with smaller metric pitches, and AT for higher-torque metric-pitch power transmission, while ISO 13050 curvilinear profiles are picked when noise, high torque, or shock load dominate [S8].
Selecting between them follows four criteria, all anchored in the standard's seven mandatory characteristics: (1) pitch, since the T/AT pitch series are fixed and not step-adjustable; (2) belt material, because the tabulated force ratings assume polyurethane with fine steel cord and drop out of scope otherwise [S3]; (3) pulley quality grade, with the standard's clauses governing runout and angular error; and (4) whether the application needs positive indexing, where AT is often preferred for its higher tooth count per unit pitch diameter. Open belts with thermoplastic polyurethane and field splicing are explicitly permitted for conveyor service but lose the standard's tolerance guarantees across the splice [S3].
Failure modes, splicing limits, and what the standard does not cover
The standard draws a hard line on belt construction: the force values are valid only for polyurethane belts with high-tension fine steel cord, so any substitution (aramid cord, glass-fibre-reinforced rubber, kevlar) voids the published ratings until a new value is agreed between user and manufacturer [S3]. This is the most common silent failure mode in the field, where a maintenance shop substitutes a rubber belt for a worn polyurethane one and finds the published service life no longer applies.
Second, spliced endless belts made from open TPU belts are accepted for conveyor duty, but the tolerances in the standard do not govern the splice zone, which means pitch accuracy across the splice is the splicer's responsibility, not the standard's [S3]. Third, the standard does not cover the higher-load curvilinear HTD/RPP family; that is ISO 13050 territory, and designers must read both standards when a machine carries mixed-profile sections [S7][S8]. Fourth, ISO 17396 specifies principal characteristics, not full design life, lubrication, or environmental derating; those come from the belt manufacturer and from application standards referenced by it. The standard's pulley quality specification does, however, give the runout, angular, and eccentricity limits that any post-machining inspection must enforce.
Forces, materials, and data points to anchor a spec
Across the two withdrawn editions, the concrete anchors available to a specifier are: ICS 21.220.10, technical committee ISO/TC 41/SC 4, 18 pages, seven mandatory characteristic groups, and T/AT belt construction defaulted to polyurethane with fine steel cord [S1][S3]. The 2014 edition was published 2014-01-16 and withdrawn 2017-11-24, while the 2017 edition was published 2017-11 and is also withdrawn, both pointing to ISO 17396:2024 as the current revision [S1][S3].
For designers, the most quotable clause is that the standard's force values are only valid for polyurethane belts with high-tension fine steel cord, and that any alternative tensile cord requires a user/manufacturer agreement on substitute values [S3]. For pulley inspection, Section 11.1.3 of the standard is the geometry-of-record for the T profile groove, including tooth angle, depth, and the flank tolerances that control mesh quality [S4]. When the design needs a higher data density than the standard provides, the manufacturer's own product catalogue fills the gap, and ISO 13050 should be added to the spec for any curvilinear-profile sections on the same machine [S7][S8]. Designers specifying pulleys for industrial drives can cross-reference the broader industrial valve and flow-meter families and pressure transmitter sections when the belt drive sits inside a packaged skid.
Closing signal: ISO 17396:2024 is the live revision to specify against, with ISO 17396:2017 drawings still accepted for spare pulleys on installed equipment; any new metric-pitch trapezoidal design should call out Section 11.1.3 groove geometry, the pulley quality clause, and the polyurethane/steel-cord construction limit in one line, with ISO 13050 added for any curvilinear sections on the same drive train. For related specification context, see the dial-indicator measurement primer where pulley runout inspection is set out against ISO 17396's quality clause.
For component-level specifications, see construction machinery and equipment.