The LiftMaster 71-1550B18LGH Sprocket Kit is an OEM replacement drive sprocket for LiftMaster commercial door operators that use ANSI #50 roller chain. Identified as 50B18, this sprocket has 18 teeth and a finished 1-inch bore with a 1/4-inch keyway to fit keyed operator shafts on applications such as jackshaft, trolley, and gearhead units. It transmits torque from the operator to the door system, supporting reliable motion control and ratio tuning where an 18-tooth #50 sprocket is specified.
Engineered for #50 chain pitch, the 50B18 tooth count provides a balanced blend of speed and torque as defined by the operator’s drive ratio. The kit includes set screws for shaft retention and alignment. For compatibility, match the sprocket’s 1-inch keyed bore and #50 chain requirement to the operator’s specifications and consult the LiftMaster manual for your model. Installation should follow lockout/tagout procedures: de-energize the operator, relieve chain tension, align the sprocket with the mating sprocket, insert the key, seat the sprocket on the shaft, tighten set screws to the manufacturer’s guidance, and verify chain alignment and tension. After installation, test door travel and safety devices before returning the system to service. Common search terms: LiftMaster sprocket kit, 50B18 sprocket, ANSI #50 chain sprocket, 1 inch bore sprocket, 1/4 inch keyway, commercial door operator replacement part, jackshaft opener sprocket, OEM LiftMaster sprocket.