Dormer G136 Series High-Speed Steel Single-End Countersink, Uncoated (Bright) Finish, 3 Flutes, 90 Degrees, Round Shank, 6 mm Shank Dia, 10 mm Body Dia. Creates a 90-degree countersink that accepts a flat-head fastener so it sits flush with the surface Three flutes provide better chip clearance than four flutes to prevent clogging High-speed steel (HSS) provides hardness for wear resistance Uncoated (bright) finish has no additional surface treatment or coating for cutting soft ferrous and nonferrous materials Single-ended tool has a round shank that accommodates most drill chucks