ISO 19347:2015 specifies the principal characteristics of synchronous endless belts and pulleys for use in synchronous endless belt drives[1] for mechanical power transmission and where positive indexing or synchronization is required.
The principal characteristics includes the following:
a) belt nominal tooth dimensions,
b) belt length and width dimensions and tolerances,
c) belt length-measurement specifications,
d) pulley grooves dimensions and tolerances,
e) pulley dimensions and tolerances,
f) pulley quality specification.

[1] These drives have been known under various names in the past, for example: timing belt drives, positive belt drives, gear belt drives.