ISO 22:1991

Overview

ISO 22:1991 - Belt drives: Flat transmission belts and corresponding pulleys - Dimensions and tolerances specifies the principal dimensions and tolerances for flat power-transmission belts and their matching pulleys. The standard defines accepted belt lengths, belt widths, pulley widths, pulley diameters and related tolerances using preferred-number series. Two informative annexes provide recommended pulley crown profiles and recommended correspondences between belt widths and pulley rim widths.

Key topics and requirements

• Principal dimensions in millimetres: standardized inside lengths, belt widths and pulley geometries to enable interchangeability and consistent manufacturing.
• Preferred-number selection: belt and pulley sizes are selected from ISO preferred-number series (R10, R20 and R40) to harmonize available sizes.
• Belt lengths and widths: tables list preferential lengths and nominal belt widths with tolerances appropriate for flat transmission belts.
• Pulley widths and diameters: pulley rim widths and diameters are standardized (selected from R series) and accompanied by manufacturing tolerances.
• Pulley crown: Annex A (informative) recommends crown shapes and crown heights for different diameter ranges to improve belt tracking; crown recommendations vary with pulley diameter and, for large pulleys, rim width.
• Belt–pulley correspondence: Annex B (informative) gives ordinary recommended correspondences between belt widths and pulley widths to aid selection.
• Normative reference: ISO 3 (Preferred numbers) is referenced for the selection of standard sizes.

Applications and practical value

• Ensures compatibility and interchangeability of flat transmission belts and pulleys across suppliers and equipment.
• Useful for mechanical designers, OEMs, maintenance engineers and belt manufacturers specifying or selecting belts and pulleys for power transmission systems.
• Facilitates procurement, stocking and replacement by reducing bespoke sizes and aligning with preferred-number series.
• Helps improve belt tracking and service life by following recommended crown profiles and correct belt–pulley width pairing.

Who should use this standard

• Mechanical design engineers specifying belt drives for conveyors, machine tools and industrial drives.
• Component manufacturers (belts and pulleys) for production tolerancing and quality control.
• Maintenance and reliability teams selecting replacement belts or upgrading drive components.
• Procurement teams standardizing spare-part inventories.

Related standards

• ISO 3:1973 - Preferred numbers (normative reference used by ISO 22 for size series selection).
• Work prepared by ISO/TC 41 (Pulleys and belts) provides the technical basis for the standard.

Keywords: ISO 22:1991, flat transmission belts, pulleys, belt drives, dimensions, tolerances, belt widths, pulley diameters, crown, preferred numbers.