Starrett D0412 4-1/2-Inch Diamond Grit Edge Hole Saw Effective cutting of hardened steels, fired ceramics, aggregate containing concrete, non-metallics and other difficult to cut materials Clean accurate cuts and extended life Uniform synthetic diamond grit bonded over a durable stell platform Always use a coolant and start with low or recommended speed and increase as ease of cutting is noticed while avoiding heat build up Recommended cutting speed is from 100 to 200 RPM