Cobalt steel zero-flute countersinks provide good wear resistance when machining hard materials at high speeds. Zero-flute countersinks have a single flute that passes through the center of the countersink. This minimizes vibration and chatter during use and prevents chips from sticking to the tool. Zero-flute countersinks leave smooth, clean edges on holes and are used to expand the top of an existing hole in a workpiece to ensure screws install flush with the surface of the workpiece. They are commonly used for installing aluminum frame storefronts, glass and window design, and architectural metalworking applications.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.