A first axial abutment surface (6) formed at the free end of an annular lip (5) of a threaded male element (1) and a second axial abutment surface (9) formed at the end of a housing (7) of a threaded female element (2) have a same axial half-sections (S) the inclination of which varies progressively in the radial direction. Such a configuration of the axial abutment surfaces optimizes the radial thrust exerted on the end of the lip depending on its thickness, in order to obtain an increased radial interference between the respective sealing surfaces (10, 12) of both elements. Application to hydrocarbon wells.