Yato Single End Screwdriver Bits S2 1/4" X 50mm Pz2 10Pcs with model number YT-78155 are equipped with precision tips for screwing bolts and screws. It is made of cold forged S2 steel, which is the hardest, most ductile and longest wearing steel. These screwdriver bits are protected with anti-corrosion coating and can also be used with a milling machine. The finishing has been done with sandblasting, which clean the surface mechanically and chemically.