The NORTON SG R981 locking disc is ideal for grinding and finishing on contours or flat surfaces. Ceramic aluminum oxide abrasive provides an aggressive, consistent cut rate. Disc is coated with a grinding aid to prevent disc loading. Heavy Y-weight backing. Ideal for exotic and heat-sensitive metals. Speed-Lok® fastener system provides fast, tool-free disc changes. Disc locks securely to back-up pads by twisting. TR disc has rubber-threaded hub.