“Shaft Loc” Quadrants are stamped of heavy gauge steel and clearly indicate the position of the damper. The quadrant handle (available for either 1/2” square or round shafts) is unique in that it locks the shaft of the damper to it by means of a powerful friction holding device strong enough to cut into the damper shaft eliminating damper rattle. The shaft is easily locked with a 1/2” open end wrench. Available for square or round ducts.