Lever 3, turning about fixed axis A, is connected by turning pair B to hook 6. This hook is swung onto upper cover 1 so that lug a of the hook enters a recess of cover 1. Flat spring 5 is arranged between covers 1 and 2. The double cover, comprising covers 1 and 2, is locked by turning lever 3 clockwise about axis A. Spring 5 ensures tight fitting of cover 2 to the shoulders on walls 4.
$324$SL,SD$