Transmission belts cover the full range across industry.  Leather Nylon belts are primarily used in heavy duty applications, for example -  for flat pulley drives up to +- 600 kw. The belts have a high tension Nylon core, covered with a chrome leather layer on either one side or both sides depending on weather a single or double sided drive is required, the Nylon comes in various thicknesses. The correct belt is usually calculated according to the parameters of the machine.