Aluminum oxide, vitrified bond for ferrous metal. Available 36, 60 and 80 grits. They come in sizes 5", 6" and 8". Designed for industrial use. Best use for sharpening tools, shaping, grinding and polishing metalAluminum oxide, vitrified bond for ferrous metal. Available 36, 60 and 80 grits. They come in sizes 5", 6" and 8". Designed for industrial use. Best use for sharpening tools, shaping, grinding and polishing metal