V-belt pulleys and idlers, also called sheaves, fit compatible V-belts in their V-shaped grooves to transmit rotational power to a shaft. Variable-pitch V-belt pulleys adjust the width of the groove, or pitch, to accommodate speed changes. Stepped V-belt pulleys have multiple grooves at differing diameters, allowing for speed changes. V-belt idler pulleys maintain belt tension and position belts away from obstacles.