the shape and conformation of the finished seam are determined by the design of the seaming rolls and the taper of the chuck. Roll shapes may be changed to accommodate different thicknesses of the can material. The roll shapes, the pressure adjustments of the rolls and the base plate will determine the shape, the dimensions and the integrity of the double seam. At first sight, the shape of the double seam may appear to be satisfactory, however, one or more of the internal structures may be out of limits. As a result, a hermetic seal will not be produced.