Timing (synchronous) belts mate with same-pitch timing pulleys in power transmission systems in which maintenance of speed ratio is an important design consideration. A timing pulley transmits force to the belt via evenly spaced grooves, which mate with the teeth in the belt. These same grooves and teeth prevent belt slippage. Synchronous belt drives are highly efficient. The belts come in a wide variety of materials and reinforcement materials. Imperial pitch timing belts have a trapezoidal tooth form whose spacing (pitch) is based on inch measurements.