Countersink, 82 Degrees , 1/2 in, High Speed Steel, Bright (Uncoated) High-speed steel countersinks provide good wear resistance in a wide range of countersinking applications. Single-flute countersinks are suitable for use at high speeds. They leave clean edges on holes and have a high, positive rake that reduces vibration as they expand the top of an existing hole in a workpiece to ensure screws install flush with the surface of the workpiece.Countersinks expand the top of an existing hole in a workpiece to ensure screws install flush with the surface of the workpiece. This helps prevent the workpiece material from swelling when a screw is installed in the hole and tightened down in metalworking applications. Countersinks can also be used to debur holes for a smooth finish.