Slumpy's Tarheel Tool Diamond Countersink, is designed to drill a hole that will allow your sink to sit flush and channel all water into the drain. For ease of use, the drill attachment has a 120/140 diamond grit coating. This coating enables you to produce a perfect angle for the flange of a Pop-Up drain. A 1/4-20 threaded hole found in the center of the drill is where the polymer locator lead disk is attached using the enclosed screw. The locator disk provides alignment and stability when grinding a bevel edge. Before using the Countersink, you will need to drill a hole in your glass sink with a 1-3/4 inch core drill bit. To prevent the bit from sliding and scratching the glass surface, position the locator disk of the countersink into the previously drilled hole.