Special silicon carbide grain formula is excellent for grinding masonry, concrete, stone and aggregate.Use the C24N wheel on hard to grind metal like cast iron and carbide.Soft bond for fast stock removal.Type 27., Special silicon carbide grain formula is excellent for grinding masonry, concrete, stone and aggregate.All sizes reinforced with the highest quality fiberglass for maximum safety and performance.Our unique Super-Lock??????????Hub combines both a mechanical locking system and chemical bond providing one of the safest, vibration-free designs in the industry.