UNITED ABRASIVES - SAIT 50118 3A FIBER DISC 4-1/2"" X 7/8"" 50 GRIT ALUMINUM OXIDE PREMIUM ALUMINUM OXIDE GRAIN WITH GRINDING AID. SPECIAL ALUMINUM OXIDE GRAIN TO REDUCE HEAT BUILD UP AND REDUCE LOADING. CLOSED COAT STRUCTURE FOR MORE MATERIAL REMOVAL AND BETTER FINISHING. RESIN OVER RESIN CONSTRUCTION FOR A STRONG BOND THAT IS RESISTANT TO HEAT AND MOISTURE. VULCANIZED FIBER BACKING FOR HEAVY DUTY SANDING.