The device includes a support structure (2) having an orifice (3) that delimits a seat (5) for receiving a nut (6) intended to cooperate with a locking screw (4). The seat (5) comprises an upper part (5a) and a lower part (5b), both shaped as truncated spheres and concentric to each other. Furthermore, the nut (6) has a spherical contour (11), and the screw head (15) has a lower part (15b), also with a spherical contour, and an upper part (15a) provided with a thread (17). The upper (15a) and lower (15b) parts of the screw head (15) cooperate respectively with the complementary thread (14) of the nut (6) and with the lower part (5b) of the receiving seat (5) such that, in the final phase of screwing the spherical contour (11) of the nut (6) bears against the upper spherical part (5a) of the seat (5), and of the lower part of the screw head (15b) against the lower spherical part (5b) of the seat (5).
