One-piece belt assemblies for LiftMaster and Chamberlain belt-drive openers in 7-foot, 8-foot, and 10-foot door lengths. If your belt's stretched out, cracked, or slipping, swapping it is the quickest way to get back to quiet, smooth travel. Some kits cover older pre-2001 units — check the part number listing against your manual to make sure you're getting the right assembly for your opener and rail type.