This International Standard specifies the principal characteristics of synchronous endless belts for use in synchronous belt drives for mechanical power transmission and where positive indexing or synchronization is required. NOTE Synchronous belt drives have been known by various titles, for example timing belt drives, positive belt drives, and gear belt drives. The principal characteristics include: a) nominal tooth dimensions; b) length and width dimensions; c) tolerances on these dimensions; d) length-measurement specifications. This International Standard is applicable to synchronous belt drives with pitch codes MXL, XXL, XL, L, H, XH and XXH, in both metric and inch dimensions.