Fiber Discs Abrasive Type Coated Abrasive Material Ceramic Backing Material Fiber Grit 36 Overall Diameter 4 1/2 in Coating Coverage Closed Resistance Properties Heat Connector Size 5/8 In.-11 Connector Type Threaded Hole Color Purple Features Grinding Aid to Reduce Heat and Extend Abrasive Life Rigid Backing Improves Grain Retention in the most Demanding Applications