The weather protection grid, System 511L, from MLL Hamburg, is a ventilation grid made of aluminium with a free ventilation cross section of 52%. The system 511L is equipped with a Z-slat of the light series of type 010L, which in turn is installed in the overlying Frame 501 by means of a proven clip technology. The slats fastened with the MLL clip system are also removable afterwards for repair work on on the facade or similar purposes.