Insert screwdriver bit set 1, material: S2 (hardness) 2, good quality 3, professional Insert screwdriver bit set Manufacture and supply various full series of screwdriver bits, nutsetters, nut drivers, sockets, socket adapters, bit holders and quick changeconnectors for screwdriver bitsmaterial types:Cr-V 6150,8660,S2Surface treatment:sandblasted, tin-coating, Cu-coating, Ni-coating, Cr-coating, ...