Gator 2-Pack 3" x 21" 40 Grit Bi-Directional Sanding Belts. Aluminum oxide abrasive material and has a cloth backing. It is suitable for use on fiberglass, metal, and wood. It is extra coarse grit and can be used on bench top sanders and power belt. Gator sanding belts are designed to fit the most popular portable belt sanders offered today. These industrial-quality belts have long set the standard for quality and value. From the durable red resin bonding system, it resists heat build-up and humidity for longer life to the bi-directional flush joint that runs smoothly in both directions.