The ROP Shop replacement (Pack of 2) Idler Pulleys for Chamberlain & LiftMaster 144C56 Garage Door Opener Specs - Refer to images 2 & 3 for more information Includes - (2) Chain Cable Idler Pulleys; comes as shown in the first image Fits garage door openers with a square rail system This idler pulley applies to tension to guide the chain cable through the end of the rail closest to the door. To make this repair to your garage door you will need a wrench set, a screwdriver and pliers to take apart and reassemble the housing, Weight: 0.08 Pounds, Manufacturer: The ROP Shop