each of these tapering surfaces come to bear against the opposite surface fig3 shows in an approximative manner the interference phenomenon which occurs when the male elements 2 3 are screwed down until abutment under pressure of the end faces 11 12 in a plane adjacent to the plane of the line x2 x2 the dashed line of the lines 14a and 15a shows the position which the generating lines 14 and 15 of the tapering convex surfaces would reach if they did notenter into contact with the tapering concave surfaces 19 and 20 as is known the phenomenon of seizing is avoided at the level of the sealing surfaces and also if necessary at the level of the threads by making use of chemical processing such as phosphate treatment with zn or mn or by depositing of metal layers such as cu ni or other surface processing different types of lubricants such as certain greases or numerous types of oil can also be used alone or together with these various deposits in the case of fig1 to 3 the existence of free annular spaces 23 24 will be noted which are provided in the interior of the sleeve between the shoulder stops 21 22 and the end of the corresponding female thread 6 7 these spaces are provided to serve if necessary to receive excess grease and to avoid an increase in pressure and thereby contribute to the lubrication of the joint in good conditions during successive cycles of.