15/64″ diameter bit for use with making a 1/4″ hole. Hex shank 3/8″ Diager Blue CERAM drill bits make clean and precise holes in granite, ceramic, quarry, tile-porcelain, glaze, tile-marble. Bits have a hex shank, two diamond segments and core extraction. and Asymmetric channel : reduces the core size for a better extraction. and New geometry : better cooling. and Profiled segment : allows a better holding by locking;. and Brazing area increased. How to use: Make a swinging movement to allow the dust evacuation. and Do not press strongly on the tool. Let it work. and Drilling with water increases the lifespan of the tool. Sharpening refreshes the cutting power of the tool. and Cutting speed : DRY :11000 RPM WET : 3000 RPM minimum. and and Use drilling guide or start drilling with a 45° angle / Use water lubrication.