The sealing design of C-FLEX™ metal C-rings is based on the elastic deformation of a metal “C” substrate which, during the compression cycle, gives a contact point on each sealing surface. The substrate characteristics determine the compressive load of the seal. This load combined with an accurate compression rate results in a specific pressure which is directly related to the sealing level obtained. A certain specific pressure is necessary to make the seal flow into the flange imperfections. In service, the system pressure supplements this load. A softer surface treatment is available to increase the plasticity of the seal and reduce the specific pressure necessary to reach the desired sealing level.