DiamondCore Rotary Tools have diamonds embedded all the way down to the shaft, not just on the outer edge. Use them on bisque, high-fired clay, glaze drips, porcelain, tile or glass. Quickly grind off glaze drips, chipped feet or sharp edges. For longevity use water, high speed and gentle pressure. "Let the Diamonds do the work." 7mm diameter. Shaft diameter 3.18mm. 80 grit ( coarse - grinding) Always use with water. Always use safety goggles. Keep water out of rotary tool motor. Use all appropriate safety precautions. Keep out of the reach of children.