Cable drum pairs available in 400-8 and 5250-18 sizes. The 400-8 is a common residential drum for shorter doors and the 5250-18 is an 18-inch drum for taller setups. Sold as a pair so you get both left and right drums. These sit on the torsion shaft and the lift cables wind around the grooves as the door opens. If the grooves are worn or the drum is cracked, the cable slips and the door hangs crooked. Pick the right drum code from the dropdown and match it to your door height, cable size, and shaft. Getting the wrong drum makes the door lift unevenly.