These 200 x 65mm double sided premium quality diamond stones give two options, just by flipping them over. We tested these extensively, medium 400G (36 micron) on one side and fine 1,000G (15 micron) on the other. Nickel plating permanently fixes the diamond particles onto the 8mm thick steel base. A chequered pattern carries away metal particles so maintaining the stone's cutting efficiency. The resulting surface is more than capable of sharpening modern hard steels, ceramic knives as well as traditional tool steels. A protective non-slip rubber surround keeps the stone in place when in use. You can use it dry but it works far better with a splash of water.