CORTOOL 1/4 Inch Dry Diamond Drill Bits is suitable for multi-purpose drilling in granite, marble, masonry, concrete, porcelain/ceramic tile, and stone etc. Diamond length is 3/8 Inch (10mm), total working depth is approx. 1.2 Inch (30mm). Vacuum Brazed diamond technology provide very high efficiency, cuts faster and lasts longer. NEW Spiral Grooved design allows quick chip removal which makes your masonry working easy. Wax inside for cooling. CORTOOL diamond tipped drill bits have wax cores built-in which automatically absorb and dissipate heat as you go. Easy to install and use with 5/8"-11 connection for angle grinder. Dry drilling and Use water for longer time. Notice: Please use with water when drilling granite and hard masonry to extend bit use-life. Diameter 1/4 Inch Diamond length 3/8 Inch Working depth 1.2 Inch 5/8"-11 Connection for using on angle grinder. Spiral Grooved design to provide quick chip removal and fast drilling speed!! Multi-purpose drilling for granite & marble, masonry, concrete, tile/ceramic, glass, hard plastic. All-Purpose Drilling Wax inside for cooling, CORTOOL Diamond Tipped Drill Bits have wax cores built-in for Cooling and Lubrication.Special Designed with Hole and Groove in the Side of Drill Bit for Removing Stone Chips Dry drilling without water. Use water for longer time Vacuum Brazed diamond technology provide very high efficiency, cuts faster, durable and sturdy.