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 or on frustoconical surfaces of large apex angle converging toward the entrance end of the socket upon assembly, respectively have one or more annular rabbets and ribs centered on the pipe axis with profiles having outer or inner flanks parallel to that axis and closely juxtaposed in the fully assembled position in which the top of each rib abuts the bottom of an associated rabbet.