DeWALT DW5570 Drill Bit, Spiral Flute, Round Shank, 3/8 in Dia Shank
  Featuring diamond-welded tips for long life and extreme durability, DeWALTA(R) tile drill bits power through dense tile, solid-body porcelain and more. Reverse-spiral threads enable continuous water cooling for quick, clean drilling. Core ejection slots remove plugs for repeated cuts.