Generic Replacement Gear, fits all chain drive and belt drive models from 1984 to current Replacement gear for Chamberlain, LiftMaster & Sears openers (1984-2002). Part number 41A2817 drive gear Includes gear and grease. Compatible with ALL fail safe units from Liftmaster, Chamberlain, Crafstman, Sears, Master Mechanic and Wayne Dalton (See List Below) This includes factory installation instructions. Drive Gear Bore Size: 1/2" Drive Gear Outside Diameter: 2 3/4" Drive Gear Number of Teeth: 32 Original manufacturer replacement part for Sears Craftsman, Chamberlain, LiftMaster, Master Mechanic Fits these Chamberlain Models: 1100, 1200, 2100, 2200, 4100, 4200, 4893OD, 5100, 6200, 710WHC, 711WHC, 7200, 7220, 7320, 7420, 7520D, 8100, 8100M, 8200, 9200, CG40, CG40D, CG42D, CSO, HD200D, HD600, PD100, PD200, PD210, PD210D, PD212, PD212D, PD600, PD610, PD610D, PD612K, PD612KLD, PD752, PD752D, PD758D, PD758S, WD822K, WD822KD, WD822KS, WD912K, WD912KS, WD922K. Fits these LiftMaster Models: 985, 1240, 1240R, 1245, 1245R,