The recess (12) between the main connecting part (8) and a collar (9) contains a toroidal or otherwise shaped sealing ring or joint (3) and the end of a tube (1) incorporating an outer flange (2), whose thickness becomes zero at the crushing bulge (4) of the sealing ring (3). An excellent seal is ensured at this location, even for pressurized fluids, and the assembly can easily be dismantled.