Garage Door Opener Drive Gear Fits Sears Fits Craftsman Chamberlain 81B0045 ( MDR ). One New Aftermarket Garage Door Opener Drive Gear 81B0045 Same as Gear in Repair Kit: 41A2817 & 41C4220A Bore Size: 1 2" Number of Teeth: 32 Outside Diameter: 2 3 4" For Garage Door Operation models 1984 present. PLEASE NOTE: This is for the Gear only. You will need to provide the Gear grease (failure to grease the Gear will result in it stripping out) If your Garage Operator runs when the button is pushed, but the Garage Door will not open, this is the Gear that is most likely the part that needs to be replaced. For models with: LiftMaster, Sears, Chamberlain, Fits Craftsman, Garage Master, Security +, Access Master, Estate Series, Master Mechanic, Formula I, Raynor, Whisper Drive, Wayne Dalton, Billion Code, Power Drive and more. Compatible with LiftMaster & Chamberlain Chain Drive Garage Door Opener models: 140, 150