Abstract: Extension (1) of a coaxial cable core (21) made of a tube. This extension is characterized by the fact that it includes a cylindrical socket (2) with tapered end (4) of a diameter larger than the inner diameter of the tube and made flexible by longitudinal slots (6), a polygonal nut (10) of which angles (11) are introduced in longitudinal slots (6) of socket (2), a traction screw (12) which is screwed into the nut and includes a pick-up end (16); this traction screw abutting against the tube, after introducing the nut into socket (2), then this socket in core (21), thus pulling the nut longitudinally to push apart and tighten the flexible tapered section on core (21) inner wall (21').