Insert screwdriver bit set 1, material: 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