The spring-loaded bolts (3) are movable into a de-locking position by a lifting device against the force of the springs (7). Each bolt is movable from the de-locking into a locking position by the spring force, independently of the remaining bolts. All springs have a decreasing characteristic and/or form a module of an integral type. Both the bolts and the loading springs may be located in a row next to each other. Typically all the springs are identical. The module may consist of a strip bent into a spring shape and divided into spring sections.
