The longitudinal connecting member assembly 1, best illustrated in FIGS. 1-4 is elongate, with the outer coil-like member 4 being made from metal or metal alloys or other suitable materials, including plastic polymers, PEEK and UHMWP, and the inner cylindrical core 8 also made from plastics, such as polyurethanes, or metals, preferably from a metal or metal alloy that is coated or covered with a t