【HIGH QUALITY HSS & CR-MO】: The drill bits of this extractor set are made of high speed steel. The reverse spiral groove design bends downward to provide maximum grip. 50-Piece Screw Extractor and Drill Bit Set, Multi-Spline Extractors, Bolt extractors, Drill Bits and Stripped Nut Remover for Removing Broken Studs, Bolts, Socket Screws, and Fittings.