SBB-3 Sure Stop for 3-inch track, Sold as a matched pair. Works with standard lift, hi-lift, and vertical lift configurations and handles doors up to 2,200 pounds. If you are running 3-inch track, you cannot use the 2-inch version because the Sure Stop has to match the track width to engage properly. They are cable safety devices that catch the door if cable tension drops suddenly from a break or the cable jumping off the drum. Common on commercial loading docks, warehouses, and heavy industrial doors. Confirm your track width is 3 inches and check the door weight against the 2,200-pound limit.