Artu - 13-Pc. Multi-Purpose Drill Bit Set Multi-Purpose Drill Bit For Rotary or Percussion Drilling For use on Glass, Granite, Plexiglass, Marble, Ceramic Tile, Fiberglass, Cast Metal, Brick, Hardened Steel, Masonry, Soft Wood, Concrete, Hard Wood. Chrome vanadium steel shank for enormous strength and flexibility. Ideal for cordless drills, corded drills and drill presses. Flat bottom parabolic flute for faster waste removal. Special negative back grinding enables the tip to bore through materials with a filing action, not cutting. Outlasts regular carbide tipped bits. No center punch needed, eliminates walking. Resharpen on a high quality silicon carbide grinding wheel. Conforms to ANSI standards. Coolants: turpentine, light oil, water.