Sungold Abrasives 4-Inch by 24-Inch 100 Grit Portable Belts Premium Industrial X-Weight Aluminum Oxide, 10 Belts/Box.   Made with ultra-thin nylon reinforced mylar tape joint, so the belt will not bump.  The belt can be run in either direction, so save time by avoiding the need to orient the belt direction.  Backing is a polyester/cotton blend, a technology introduced by Sungold, that gives the strength of polyester, but employs cotton yarns to prevent the stretching that can occur with all polyester backings.  While many belts will tear or shread from nails and staples, the backing employed by Sungold resists tears.  Resin on resin bond used to adhere the grains, using high temperature resitant resins, to hold up to high heats generated by belt sanders, provides extended belt life compared to other belts.