This Montolit Diamond Drill Bit is made in Italy with high quality diamond construction ensuring the Bit will quickly drill many holes (up to 25 or more). Bit can be used on the hardest porcelain, ceramic, natural stone (granite, marble, slate and limestone), terra cotta and glass. Bit is designed to fit on any 3/8" rotary drill (NOT hammer drill) with a recommended drill speed of 800 rpm minimum. Average drill time is 20 seconds per hole.