Abstract: A joint for casing tubes comprises a pair of tubes each having an external threading on at least one end, and hollow sleeve having corresponding internal threading on both ends. The internal threading of the sleeve on each end terminates in an annular seat which extends radially inwardly and axially toward its corresponding end of the sleeve, and thus has a frustoconical shape. The end surface of each of the threaded ends of the pair of tubes is correspondingly shaped. The threading on the sleeve and pair of tubes is so configured that when the sleeve and tubes are interassembled the crest of the internal threading of the sleeve will contact the root of the external threading on the tubes, whereas the crest of the external threading on the tubes will be spaced from the root of the internal threading on the sleeve.

Abstract: Hermetic metal pipe joint, comprising a male element with at least one external tapered thread and a female element with complementary internal threads. An end part of the male element beyond each thread has a conical seal surface and the female element has a conical seal surface with the same taper as that of the conical surface of the male element. The two conical surfaces on the male and female elements mate upon tightening of the joint. The length of the seal surface of the female element along the generatrix is greater than that of the corresponding seal surface of the male element. These two seal surfaces of the male and female elements have a taper in the range 6.25 to 9.25% relative to the axis of the conical seal surface. The length of the surface of the male element which comes into contact with the corresponding surface of the female element is between 0.5 and 2.5 mm.