These superior quality stones are made of Aluminum Oxide bonded with porcelain type clays which provide the greatest strength and rigidity required for fast stock removal and longer life. The ceramic bond controls the release of the Aluminum Oxide abrasive grains so that as each particle begins to dull, the bond discharges it allowing new abrasive grain to surface with fresh, sharp cutting edges. Guaranteed to run true. Stones are securely bonded to 3mm shanks.