the backing ring 50 preferably by brazing the backing ring 50 may include an annular ridge 52 therein contacting a lower side of the self welding member 46 during the bonding and self welding operation ridge 52 cooperates with the external tooling to ensure a highly concentrated bonding force as will be described subsequently fig2 also shows the tooling 54 that is used in this self welding operation similar tooling is used in the self welding operation for the embodiment of fig1 but is not shown in fig1 the tooling 54 includes an upper tool 56 that is generally hollow and of the required shape to conformably fit over the first housing 28 which is cylindrical in the preferred case the cylindrical diameter of the upper tool 56 is selected to fit over the body of the first housing 28 and against the first peripheral flange 32 more specifically a force concentrating annular ridge 58 of the upper tool 56 contacts the upper side of the first peripheral flange 32 the annular ridge 58 of the tooling is positioned in opposition to the annular ridge 52 of the second flange self welding member 46 these ridges concentrate the force applied externally to effect the bonding into a small annular area of the facing and contacting surfaces of the members 34 and 46 the concentrated pressure ensures a close contact of these members 34 and 46 along a corresponding annular sealing surface around the entire periphery of the members 34 and 46 the close high pressure contact results in a hermetic weld between.