1/2" Inch 12.9 mm DiamondSure Diamond Drill Bit Hole Saw for Glass, Tile, Granite, Ceramic, Porcelain, Stone Bonded Diamond Grit: Electroplate bonded diamonds for optimum diamond life. Nickel Plated: Reduces bit friction and heat build-up and inhibits rust. Grooved Tip Edge: Provides maximum surface area & increases water "churn" for tip lubrication. Tip Lubrication Hole: Provides optimum tip lubrication by allowing water flow in and out of bit. Core Extraction Hole: Special holes in back of the "Bell" allow easy removal of cores or plugs.