PCD (poly crystalline diamond) mills, made of bonded diamond crystals affixed to carbide shank, handle nonferrous metals, and feature coolant through design. CBN (cubic boron nitrate) mills are formed through sintering so they can machine hard steels to 66 Rc as well as hard castings, Inconel, Monel, and Stellite. Mills are available from stock in ball nose, torus, and flat end designs, in sizes from 3/16-1/2 in.