Hitachi 728026 5/16-Inch Diamond Core Bit Glass and tile bit measures 5/16-inches in diameter Drill bit drills through glass, marble, class 5 porcelain, granite and slate Constructed of hardened and tempered thin wall alloy steel Requires water lubrication during use Comes with a 30-day limited warranty 5/16" Diamond Core Bit Drill through Porcelain, Marble, Slate and Glass Water Feed Needed Drill up to 30-35 Holes Diamond Grit