Coupling element for coupling two portions to be coupled (501, 501') of at least one tie rod, said coupling element comprising: a body comprising two opposite side openings (23', 23") for the passage of a respective portion to be coupled (501, 501') of said at least one tie rod, said openings being arranged along a first longitudinal axis (x), a pin arranged along a second transversal axis (y) substantially perpendicular to said first longitudinal axis (x), said pin comprising at least one slot adapted to insert said portions to be coupled (501, 501'), said pin being arranged between said side openings (23', 23") and being coupled to the body in a rotatable manner so as to be able to rotate on itself around said second transversal axis (y), and locking means for locking said pin on said body so as to prevent its rotation on said second transversal axis (y) along at least one rotational direction, wherein said pin comprises at least a shaped base, said coupling element being characterised in that said locking means comprise at least a pair of worm screws arranged on said body along a direction parallel to said longitudinal axis (x) and surrounding said shaped base, said worm screws having a complementary contour to the toothing of said base of said pin and configured in such a way that during use, rotation of said shaped base is allowed only when an outer torque is applied to said worm screws along a predetermined rotational direction (φ), placing them in rotation, and in such a way as to prevent their inverse rotation in the direction opposite to said predetermined direction (φ) so that during use, when said portions to be coupled (501, 501') are inserted into said slot and overlapped one another after passing through a respective side opening (23', 23"), said portions to be coupled (501, 501') are coupled together by rotating said pin on said second transversal axis (y) and subsequent locking by said worm screws. a body comprising two opposite side openings (23', 23") for the passage of a respective portion to be coupled (501, 501') of said at least one tie rod, said openings being arranged along a first longitudinal axis (x), a pin arranged along a second transversal axis (y) substantially perpendicular to said first longitudinal axis (x), said pin comprising at least one slot adapted to insert said portions to be coupled (501, 501'), said pin being arranged between said side openings (23', 23") and being coupled to the body in a rotatable manner so as to be able to rotate on itself around said second transversal axis (y), and locking means for locking said pin on said body so as to prevent its rotation on said second transversal axis (y) along at least one rotational direction, said pin comprises at least a shaped base, said coupling element being characterised in that said locking means comprise at least a pair of worm screws arranged on said body along a direction parallel to said longitudinal axis (x) and surrounding said shaped base, said worm screws having a complementary contour to the toothing of said base of said pin and configured in such a way that during use, rotation of said shaped base is allowed only when an outer torque is applied to said worm screws along a predetermined rotational direction (φ), placing them in rotation, and in such a way as to prevent their inverse rotation in the direction opposite to said predetermined direction (φ) so that during use, when said portions to be coupled (501, 501') are inserted into said slot and overlapped one another after passing through a respective side opening (23', 23"), said portions to be coupled (501, 501') are coupled together by rotating said pin on said second transversal axis (y) and subsequent locking by said worm screws.