This TCT countersink clamps onto any drill between 3.0mm & 7.2mm in diameter. Recommended for wood & 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 & not suitable for ferrous & non-ferrous metals.