This International Standard specifies the principal characteristics of metric pitch curvilinear synchronous endless belts and pulleys in G, H, R, and S profile systems for use in synchronous belt drives (also known in the past as timing belt drives, positive belt drives, gear belt drives) for mechanical power transmission and where positive indexing or synchronization might be required. The principal belt and pulley characteristics include the following: a) nominal belt tooth dimensions; b) belt tooth pitch spacing; c) belt length and width dimensions and tolerances; d) belt length measurement specifications; e) pulley groove dimensions and tolerances; f) pulley diameter and width dimensions and tolerances; g) pulley quality specification