Carbide Bur - Ball Shape, MICRO Cut - 3/8" x 5/16" x 1/4" Shank - SD-3 Almost all materials up to a hardness of 940 HV (68 HRC) can be machined. They maintain their geometry over the entire service life, and are well suited to manual and machine applications. They offer a higher stock removal rate and produce a high surface quality, particularly compared with conventionally milled surfaces..