TR discs have threaded central hubs that require two-and-a-half turns and mount to Norton TR or 3M Roloc TR back-up pads * Ceramic aluminum oxide is a self-sharpening grit that is harder, tougher, and lasts longer than aluminum oxide * "Supersize" lubricant helps cut faster and cooler for an improved workpiece finish * 1-ply laminate disc for flexibility, in order to conform better to the workpiece * Used with a molded rubber or foam backing pad (sold separately)