When rubber belts reach a thickness of 2 inches (51 mm) or for rubber belts ordered at 2 inches (51 mm) thick, the amount of lengthwise tension required to insure best performance is ½ inch (13 mm) of stretch of the 12 inch (305 mm) marks placed on the belt edge. Failure to apply sufficient lengthwise tension to a rubber belt will often greatly reduce the capacity of the belt to shrink, cause generalized light corrugations in some shrunk fabrics and may result in the occurrence of cracks on the belt interior.