The Mercer Industries type 27 single grit Depressed center grinding wheel for metal is made with 24 grit aluminum Oxide throughout the wheel. Formulated to grind ferrous metals at any angle. Internally reinforced for safety and strength. Wheel is balanced to avoid vibrations. Available in 4", 4-1/2", 5", 7" and 9" diameters with a 5/8", 7/8" or 5/8"-11 Arbor to fit all angle grinders.