3M coated 577F Type 27 flap disc uses alumina zirconia as the abrasive material and has a diameter of 4 1/2 in. 3M incorporates this alumina zirconia material into the flap disc forming a grit of 80. 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 flap disc can be run at a maximum speed of 13300. The 3M flap disc uses fiberglass for the backing plate.