Abstract: Two metallic pipes to be sealingly interfitted are respectively provided with a plug-shaped male extremity and a socket-shaped female extremity having mating frustoconical peripheral threads and adjoining unthreaded annular peripheral formations closely contacting each other upon assembly. An annular end face of the male extremity and a confronting annular shoulder of the female extremity, lying in planes transverse to the pipe axis, have spiral tracks of trapezoidal profile engaging each other with close positive fit in the fully assembled position, the pitch of these tracks being such as to counter a radial compression of that end face by the interacting unthreaded peripheral formations.