A&H Abrasives 100928, 100-pack, Sanding Discs, Aluminum Oxide, Fiber Backed, 4-1/2x7/8 Aluminum Oxide 50 Grit Resin Fiber Sander Disc Great discs for heavy grinding on metals and wood carvings with an angle grinder. Specifications: Diameter=4-1/2 in, Shape=ROUND, Bore Diameter=7/8 in Specifications: Grit=50, Abrasive=ALUMINUM OXIDE, Abrasive Bond=PHENOLIC RESIN Specifications: Backing=RESIN FIBER, Maximum Rpm=13000