Proxxon 23100 18 Piece Allen Key Socket Set, 1/4 and 1/2 Inch Drive Drive bits made from a combination of chrome-silicon-manganese-molybdenum steel and forged using 31CrV high carbon steel ensuring socket strength Double nickel plating and single chrome plated finish for optimum surface protection Bits have black oxide finish for a sure grip Socket sizes easy to read due to laser marking German engineered hand tools for the professional user