3M coated 381C fiber disc uses aluminum oxide as the abrasive material and has a diameter of 7 inch. 3M incorporates this aluminum oxide material into the fiber disc forming a grit of 16. All abrasive products that rotate or spin, such as the ones in this category, have a maximum speed at which you can run them. This 3M fiber disc can be run at a maximum speed of 8600 RPMs.