UNITED ABRASIVES - SAIT 50271 Z FIBER DISC 7"" X 7/8"" 50 GRIT ZIRCONIUM ZIRCONIUM GRAIN - PREMIUM CLOSED COAT STRUCTURE FOR AGGRESSIVE STOCK REMOVAL AND LONG LIFE. RESIN OVER RESIN CONSTRUCTION FOR A STRONG BOND THAT IS RESISTANT TO HEAT AND MOISTURE. VULCANIZED FIBER BACKING FOR HEAVY DUTY SANDING.