These 3/8 Inch X 13 Inch cloth sanding belts are made with premium German engineered Starcke material. All our belts are made custom to order in grits 24 - 400. This Aluminum Oxide abrasive grain features Poly "Y" weight back on coarser grits (24-36) and Cotton "X" weight backing on all other grits (40-400). These belts feature a butt joint for a consistent and smooth finish and extended belt life. This premium high performance abrasive is used on air file belt sanders and is excellent for all purpose sanding - and specifically for use on Aluminum, Steel, Composite, Hardwood, and Softwood.