Presta TorqKey Bit SetEngineered for long life All Prestacycle Professional bits are made with hardened S2 steel, which is much stronger than most hand tools which are made of CRV Steel. S2 steel also resists stretching, preventing rounded edges on the bits that could damage bolts. We apply nickel plating to all Professional bits to prevent marring to Stainless Steel, Aluminum and Titanium screws and to provide a long lasting finish. Specific hex bits have micro surfacing