These double flute cutters are made from solid tungsten and are to be used for clockwise cutting. The fishtail profile ensures cutting to the center, allowing boring. Usable on cast iron, hardened cast iron, steel, cast steel, brass, aluminum, and even glass, plastics and carbon fiber. The set includes one each of 1/32", 5/64" and 7/64" (1.0, 2.0 and 3.0 mm) shaft diameter.