This high-quality Corundum Grinding Stone should be used with your Portable Electric Chainsaw Sharpener or other tools. These grinding heads are made of corundum grinding stone: a rock-forming mineral, that is a crystalline form of aluminum oxide with traces of iron, titanium, vanadium, and chromium. Corundum has a hardness of 9 on the 10-point Mohs' scale. Details Sizes Available S 5/32" / 4 mm M 3/16" / 4.8 mm L 7/32" / 5.5 mm Package includes Corundum Grinding Stone x 12