Check the listing for details. KEO 55501 Countersink,60 deg.,3/16" Body 3ZUH2. Condition: New. Listed at 13.53 USD. Countersink, 60 Degrees , 3/16 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. Six-flute countersinks provide fast material removal and leave a smooth finish as they expand the top of an existing hole in a workpiece to ensure screws install flush with the surface of the workpiece. They remove more material with each revolution and typically provide more wear resistance than countersinks with fewer flutes.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 a.