Hard bond for long life grinding with fast stock removal.High performance, ceramic aluminum oxide grain, is designed to outlast standard aluminum oxide wheels.Very uniform, high density grain structure is extremely durable and self sharpening for long life and cooler cut.Type 27., Designed to provide very long life for fewer wheel changes and less downtime.All sizes reinforced with the highest quality fiberglass for maximum safety and performance.Our unique Super-Lock?âòÀÞ?â Hub combines both a mechanical locking system and chemical bond providing one of the safest, vibration-free designs in the industry.