Vertical lift cable drums, model D1100-216, for doors up to 18 feet tall on vertical lift track. Each drum holds up to 660 pounds and takes 3/16-inch max cable. Vertical lift doors go straight up instead of curving along a radius, so the drums are wound differently than standard lift drums. Sold as a left and right pair. To figure your cable length: floor to shaft center plus 234 inches, minus the door height. If the math does not match your existing cables, double-check the measurement. Wrong cable length means the drums run out of wrap or the cables go slack. Confirm door height and shaft size before ordering.