The Dormer G136 series high-speed steel single-end countersink with an uncoated (bright) finish creates a 90-degree conical opening that accepts a flat-head fastener so it sits flush with the surface. The three flutes clear chips away to prevent clogging. High-speed steel (HSS) provides hardness for wear resistance. The uncoated finish has no additional surface treatment or coating for cutting soft ferrous and nonferrous materials. The tool has a single cutting end and a round shank that accommodates most drill chucks.Countersinks are fluted cutting tools that cut a conical or gradually widened opening for a hole into the surface of a workpiece, which provides a seat for a screw or rivet head. They are also used to create center holes for a machine center, deburr surfaces, and enlarging existing holes. The countersink"s body diameter should be the same size or larger than what is being countersunk.Precision Dormer manufactures cutting tools under the brands Precision Twist, Dormer, and Union Butterfield. The company, headquartered in Crystal Lake, IL, meets International Organization for Standardization (ISO) standards 9001 and 14000.