The weather protection grid, System 691, from MLL Hamburg, is a ventilation grid made of aluminium with a free ventilation cross section of 39%. The system 691 is equipped with a Z-slat of the medium series of type 090, which in turn is installed in the overlying Frame 601 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.