Carbox nitrile roughtop yield vastly longer service life than rubber roughtop. It is ideal where regular roughtop surfaces wear down quickly and must be replaced. The 3 Ply Poly 135 Tan Carbox Nitrile RT X FS features a strong all-polyester carcass. The 3 Ply CN40 Blue Carbox Nitrile RT X Bare is a poly/nylon construction. These belts are popular for handling cardboard cartons.