WHEEL GRADE A 16 QBVery aggressive grinding, long wheel life on weldments, castings, steel and ferrous metals in heavy-duty foundry work WHEEL GRADE C 16 PBVery aggressive grinding, long wheel life on masonry, poured concrete, tilt-up panels, large aluminum castings and all non-ferrous metals. WHEEL GRADE ZA 16 RBFor optimal grinding performance, stock removal and long life on cast steel, alloy steel, malleable and ductile iron. Zirconia & aluminium oxide grains combined with high-performance resin bond.