Clamp rings have an important influence on the thermoforming process. Especially on the shaping of the sealing flange. The more precise the adaptation of the clamp ring shape to the desired article shape. The better the final product is. In particular for articles with U-rims. Clamp rings can be perfectly fitted to the finished product. Also varying foil thickness in a tool is possible with Mafox|F. Without time-consuming clamp ring changes.