BB-100 bottom brackets are what the lift cables attach to at the bottom of the door. Made from 13 gauge steel, Milford pin style. Sold as a pair so you get left and right. Dimensions are 5-11/16" tall by 2-11/16" wide with 1-3/4" side flanges. When your bottom brackets are rusted through or the cable keeps slipping off a cracked bracket, Those are the replacement. they are residential-grade so they are for standard weight doors, not heavy commercial setups. Make sure the pin style and gauge match what you are replacing.