Idler: A driven wheel that does not transmit electricity by means of a shaft. It spins freely, and most pushed pulleys are connected to other gear, such as wheels or drives, through driveshafts.
Roller: A regular pulley has a slot for a belt, chain or cable. A reel is a broader pulley commonly employed in cable programs, enabling the cable to be wound about a number of instances the diameter of the reel.
