not resiliently return to the original shape when the components of the fitting are drawn apart and the seal is broken the gasket is permanently deformed by engagement of the knife edge it should be understood that simultaneously with the events which occur on one side of the gasket a corresponding sequence of events occurs on the opposite side of the gasket fig6 shows a second embodiments of the invention absent the over tightening feature as shown in fig3 5 in this embodiment the fitting is shown at 1 2 turn past finger tight and the location of the sealing features on the tubular members are the same as those in the first embodiment an annular sealing bead 60 with an arcuate profile extends from the end wall of the tubular element and on the outside of the tubular member an annular knife edge 62 extends from the tubular element near the periphery of the tubular member in this embodiment the gasket also has the same features as shown in the previous embodiment this embodiment differs from the first embodiment in that the inner face 64 of knife edge 62 which extends towards the annular sealing bead does not intercept an end wall which is perpendicular to a central axis formed by the tubular members instead the knife edge continues to slope towards the central axis until it meets the outermost edge of the annular sealing bead 60 thus absent from the end wall of the tubular element is the flat surface which engages the flat surface of the gasket in operation as the coupling nut is turned the knife edge penetrates the flat surface of the gasket and the sealing bead exerts pressure on the beveled face.