Review on Diamond Coated Ceramic Drilling Bit 6mm-50mm by Brent Porter

I used two sets to drill some holes in a 1/4 inch thick mirror so I could put a light in the center of the mirror can install . No signs of wear after a few holes. I had a garden hose hooked up to ensure a steady flow of water. The only issue with the mirror was a small chipping of the coating on the back, but I don't blame bits for that, it's my technique. I would say for the price they are hard to beat.