LIFTMASTER Garage Door Openers 41B3869-3 Belt Drive Trolley Compatible with LiftMaster and Chamberlain Brand garage door openers 1984 thru current. Compatible with LiftMaster Chamberlain belt drive garage door opener models 1270, 1280, 1280R, 2280, 2580, 2500, 2500B, 2500D, 2585, 8100, 8100M, 8200, 9200, WD822K, WD922K, WD912K, WD912KS, WD822KS (all models may not be listed). 8550 DC Battery Backup Belt Drive If square rail assembly see part number 41C5141-1. Older part number 41B3869-1