Insert screwdriver bit set 1, material: S2 (hardness) 2, good quality 3, professional Insert ... 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, Zn-coatingHead types:PH, PZ, slot, Torx, square, hex ...