The Aluminum master lap for Diamond coated flat lap disk grinding wheel, it is only a machine accessories The Aluminum master lap is only a machine accessories. The material is 100% aluminum, no diamond coated on the surface. So that you can't using it to grinding stone directly. We recommend using the Aluminum master lap for diamond coated flat lap disk Diamond coated flat lap disk grinding wheel can be installed on the aluminum master lap. So if you want to sharpening the gemstone or steel knives, you need purchase a diamond disk(Not included, need to purchase separately), and a aluminum master lap. All our diamond flat laps wheels have a 1/2" arbor hole and are intended to be mechanically clamped to a Master Lap.The surface of the aluminum plate is smooth and the concentricity is good, Weight: 0.110231131 Pounds, Manufacturer: RTKYYZ