... : S2 (hardness) 2, good quality 3, professional Insert screwdriver bit setManufacture 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 ... :single head, double head, head with round neck,non-magnetic and magnetic