This unique tool easily and quickly forms sheet metal patches and panels into compound and custom shapes. It comes with a 1 1/2" hammer bit with . 401 shank to fit most air hammers, one # 5 lower anvil with 2 3/8" radius, and six spacer washers to adjust stroke for different gauge metals. All hammer bits and anvils are heat treated for long life. One ball valve and fitting for on/off air control is included with each unit. Just add your own air hammer, such as campbell hausfeld pl1534. These units will shape 18 gauge metal.