This part is a commercial-grade adjustable top bracket made from 12 gauge steel. It mounts on the very top of the door and helps guide the door into the track when it starts to open. The adjustable slot lets you fine-tune the alignment so the rollers track properly and the door does not bind. Sold individually, not as a pair. When your top bracket is bent or the door's catching at the top of its travel, replacing this usually helps. This one's sized for commercial doors so it is heavier than the residential versions.