<p>The unit has two axially sticking projections (10, 11) designed at a hinge unit (9), where the projection (11) is provided inside a thread (12). The projection (10) axially projects in the same direction as the projection (11), where counter teeth (8) and the projection (11) are radially separated from each other by an air gap (13). A groove (21) is radially covered between the hinge unit and a collar (6) by a cover ring (22).</p>
