In practice, in order to reinforce the effect of the central sealing means 9, 42, 43, and/or the mutual bearing of the surfaces 10-11, 44-45, 46-47 respectively and also when the connector comprises a second sealing means such as 33, if needed for possibly reinforcing the efficiency of this second sealing means, one can be led to reduce or even cancel the radial interference between the thread cre