Idler: A pushed wheel that does not transmit energy by means of a shaft. It spins freely, and most driven pulleys are related to other gear, these kinds of as wheels or drives, by way of driveshafts.
Roller: A typical pulley has a slot for a belt, chain or cable. A reel is a broader pulley commonly used in cable methods, allowing the cable to be wound close to several occasions the diameter of the reel.