1/2 inch (14mm) Diamond Coated Hole Saw Drill Bit For Making Lighted Wine Bottles and Glass Blocks This drill bit makes a perfect hole to insert a mini light string into a wine bottle or glass block. The end of this bit is grooved so the diamond coating has better adhesion for longer life and the side hole allows for water to lubricate the inside of the drill bit to insure an smooth and perfect hole. Water lubrication is strongly advised. We have used these drill bits for years on our lighted wine bottles. We can usually drill up to 25 bottles per bit!