1/4" Inch 6.5 mm DiamondSure Diamond Drill Bit Hole Saw for Glass, Tile, Granite, Ceramic, Porcelain, Stone,DiamondSure,900-003" /> they are electroplated, blonded and designed for drilling to depths of about 1/2" in ceramic tile Not designed for use on concrete, masonry, metal or for use with impact hammer drills.