PowerLock Type III discs have threaded central hubs that require two-and-a-half turns and mount to Norton TR or 3M Roloc TR back-up pads * Zirconia alumina is self-sharpening and durable, allowing for a faster cut rate than aluminum oxide * Cloth backing is stiffer, tougher, and thicker than a paper or film backing * Laminated construction provides a durable backing to help prevent shredding and snagging * Used with a molded rubber backing pad (sold separately)