Gator Grit 3 Pack 5" x 1/4" 40 Grit Extra Coarse Bolt-On Sanding Disc. The bolt on sanding disc is made of quality red resin and is specifically designed for power tool needs such as resisting heat and moisture. The disc fits backer pads with a 1/4'' center hole. For use on wood, metal, drywall, fiberglass, or painted surfaces.