[1  & 2   x 21  ]

From the Manufacturer

The toughness and enduring sharpness of Aluminum Oxide particles make the sanding belts a fine abrasive for both wood and metal. Abrasive particles are bonded to their backing with resin over resin adhesive, which means a longer wearing belt. Belts have a butt joint so are bidirectional, can be run in either direction.