This TCT countersink clamps onto any drill between 1/8 inch and 9/32 inch in diameter. Recommended for wood and man-made boards. By reversing the countersink on the drill, it can be used as a non-cutting depth stop. Ensures flutes of drill are aligned with flutes of countersink. Do not overtighten screw. Not suitable for production applications and not suitable for ferrous and non-ferrous metals.