Overview
ISO 19347:2015 - "Synchronous belt drives - Imperial pitch trapezoidal profile system - Belts and pulleys" specifies the principal characteristics of synchronous endless belts and pulleys used for mechanical power transmission and where positive indexing or synchronization is required (timing belt / gear belt drives). The standard covers belt tooth geometry, pitch systems in imperial units, dimensional tolerances, measurement methods and pulley groove and quality requirements.
Key topics and technical requirements
- Profiles and pitches: Seven trapezoidal profiles are standardized - MXL, XXL, XL, L, H, XH, XXH - with defined pitches (in mm and inches), e.g. MXL 2.032 mm (0.080 in), XL 5.080 mm (0.200 in), L 9.525 mm (0.375 in), up to XXH 31.750 mm (1.250 in).
- Belt tooth dimensions: Nominal tooth geometry for single- and double-sided belts (Types A - symmetrical, and B - staggered) with specified tooth form.
- Length, width and height dimensions and tolerances: Standardized pitch lengths, belt widths/heights and tolerances for different profiles and length ranges; tables list standard pitch lengths and corresponding number of teeth.
- Belt length measurement: Defined measuring fixture and total measuring force requirements to ensure repeatable pitch-length verification.
- Double-sided belt tolerances: Positive length tolerance = 1.5× the equivalent single-sided tolerance; negative tolerance = 2× the single-sided tolerance.
- Pulley groove and pulley dimensions: Groove geometry (involute and straight-sided), pitch-to-pitch tolerances, pulley width/diameter tolerances and other critical tolerances for mating belts and pulleys.
- Pulley quality specification and designation: Quality, finish and balance requirements; standardized methods to designate belts and pulleys for procurement and documentation.
- Normative annexes: e.g., flange dimensions are included.
Practical applications and users
ISO 19347:2015 is intended for:
- Mechanical designers and OEMs specifying synchronous belt drives for conveyors, printers, robotics, automotive ancillaries, machine tools and indexing systems.
- Belt and pulley manufacturers ensuring interchangeability and conformity to imperial pitch trapezoidal profiles.
- Procurement, quality and test engineers verifying dimensional compliance and measuring belt/pulley assemblies.
- Maintenance and service teams replacing timing belts and pulleys in equipment requiring accurate synchronization.
Using ISO 19347 helps ensure reliable power transmission, correct fit between belts and pulleys, predictable performance and simplified sourcing of compatible components.
Related standards (if applicable)
- ISO 254 - Belt drives - Pulleys - Quality, finish and balance (normative reference)
- ISO 1101 - Geometrical product specification (GPS) - Geometrical tolerancing
Keywords: ISO 19347, synchronous belt drives, timing belt, imperial pitch, trapezoidal profile, belts and pulleys, belt dimensions, pulley grooves, pitch length, tooth profile.