XL Thickness Disc Premium Blue Fired Aluminum Oxide A3 grain with a Active grinding agent and Polyester heat treated backing. Contaminate-free and provides rapid stock removal and extremely long life. A3 Can be used on ferrous metals (alloyed and unalloyed steels, high speed steel, cast iron), stainless steel, non-ferrous metals (aluminum, brass, copper, zinc) as well as on composites, plastics, and soft and hard woods.