SBB-2 Sure Stop devices for 2-inch track, Sold as a matched pair. Those are cable safety brackets that stop the door from free-falling if a lift cable breaks or comes off the drum. They work on standard lift, hi-lift, and vertical lift configurations. Rated for doors up to 550 pounds. The Sure Stop grabs the track when cable tension drops, which prevents the door from slamming down. If you are running a commercial door or a heavy residential setup without safety stops, This product is the add-on that keeps the door from becoming a hazard. Make sure you've got 2-inch track before ordering.