Abstract: A box member and a pin member each have a tapered thread, an abutment end face and a shoulder for engagement respectively with shoulder and end face of the other member, one coacting surface pair being conical, the other one being planar. Shoulder and end face are spaced differently in the two members such that upon engagement of a conical shoulder and end face, planar end face and shoulder have a gap of about 0.5 to 2.5 per cent of the spacing. Taper/bulge seals are provided adjacent the abutment surfaces to be effective before the planar surfaces abut as the joint is made up. The effective pitch diameter of the pin member remains consistently smaller than the pitch diameter of the box member, at least up to an insertion of the pin member so that the planar surfaces abut.

Abstract: Box and pin members have two axially spaced thread sections being separated by a radial step zone which includes, for one member e.g. the pin member, an annulus having an axial undercut, a frusto-conical end face and a radially outwardly bulging peripheral surface, which sealingly engages a slightly contoured inner surface of the box member in the step zone, while the end face of the annulus bears against a complementary face in the step zone of the box member. These stop faces supplement complementary thread stop faces respectively at the end of the pin member and in the box member. In a second example, the end face of the annulus is spaced from the box member and the flange of sealing sleeve is interposed, while the sleeve itself is situated in the undercut.