Check the listing for details. KEO 55416 Countersink,82 deg.,1/2" Body 3ZTR5. Condition: New. Listed at 22.90 USD. Countersink, 82 Degrees , 1/2 in, Cobalt, Bright (Uncoated) Cobalt steel countersinks are harder than high-speed steel countersinks and provide good wear resistance when machining hard materials at high speeds. Single-flute countersinks are suitable for high-speed countersinking operations. 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 us.