Fiber Disc Abrasive Type Coated Abrasive Material Ceramic Backing Material Fiber Grit 36 Overall Diameter 4 1/2 in Series RazorStar F990S Maximum Operating Speed 11 000 RPM Resistance Properties Tear Connector Size 7/8 in Features A Single Discs Design has been Optimized for Superior Performance on all Materials Including Carbon Steel Aluminum Stainless Steel and Hard-to-Grind Metals Engineered Shaped Ceramic Grain Technology Deliver Unbeatable Grinding Performance Grade Coarse