Chamberlain 41B5424 Garage Door Opener Belt Idler Pulley Genuine Original Equipment Manufacturer (OEM) Part Compatible with LiftMaster garage door opener Estate Series belt drive models 2580, 2585, 3585, 2500, 3500, 2500B, 2500D (all models may not be listed). 8550 DC Battery Backup Belt Drive For use on LiftMaster Belt Drive Models 2500, 2580, 2280, 3280 and 3500D. For use on Chamberlain Belt Drive Models WD822K, WD922K and WD912K.