Power transmission belt sheaves or pulleys are used to transfer mechanical power. They include synchronous, timing, v-belt, variable pitch, flat, and round sheaves.  Timing sheaves have external teeth that interlock with the teeth of a timing belt to transmit high torque. Timing belt sheaves are commonly used in automobiles where the timing belt connects the crankshaft and camshaft to control engine valves. Variable pitch sheave systems have one sheave attached to the driving motor shaft and connected to a driven or companion sheave.