[en] The Wendelstein 7-X (W7-X) superconducting coils will be subjected to high electro-magnetic forces and moments during the stellarator operation. It is therefore essential to prove that the mechanical connections which keep the coils joined together and linked to the magnet system Central Support Structure (CSS), are capable to take the operational loads during the machine lifetime, with thousands of load cycles. Critical connections, identified by the finite element (FE) analysis of the magnet system, are the bolted Central Support Elements (CSE) between coils and CSS. Each CSE is composed of a matrix (usually 3 x 3) of parallel bolts. They are tightened in order to highly pre-compress the contact flanges between coils and CSS. The FE analysis shows high loads in particular on the Non Planar Coil type 1, which is called NPC1Z1. This critical connection was studied by using mock-ups. Each mock-up, made of the same materials as in the real W7-X, was actually composed of a row of 3 bolted elements, i.e. one third of the real connection which shows a 3 x 3 bolts matrix. The mock-up was subjected to the scaled-down dominant forces and moment derived from the FE calculations. The tests were carried out at 77 K (while the real CSE will operate at 4 K), and consisted in applying the forces starting from zero and ramping them up to a given set point, so simulating the coil current ramp-up and ramp-down. The loading steps were repeated for more than 4000 cycles, in order to reproduce the entire W7-X lifetime. At the end of these cycles, high load cycles were performed, with the set points increased above the nominal loads (i.e. those corresponding to the '' 3 Tesla case '') with the aim to explore the limit of such bolted connection. The tests showed that the mock-ups could take the nominal loads, but that at 120% of such loads, plastic failure occurred on the mock-ups. Stick-slip phenomena on sliding contacts were also observed. This paper presents details on the design and assembly of the CSE, on the test mock-ups and test device, on the execution of the test, and on the results and main conclusion of the experimental campaign. (author)