Center bearing support bracket, 11 gauge steel, with a 3-3/8" bearing and 3-3/8" shaft offset. This goes in the middle of the torsion shaft to keep it from sagging or wobbling on wider doors. Without it the shaft flexes during cycling and that puts extra stress on the springs and drums. If you hear a vibration or the door's not lifting evenly, a worn center bearing could be the cause. Sold individually. Match the bearing size and shaft offset to your current setup before ordering because these come in different sizes.