Am element for walls supporting a plurality of idle rollers, particularly for accumulation stations for conveying lines for products in general, comprises two components coupled together, said components being identical in the case of central walls, and different in the case of side walls, one of said different components being identical, i. The density correction unit corrects printing data corresponding to the dot printing line printed by the nozzles including the abnormal nozzle and printing the same line as the abnormal nozzle so as to be close to densities of other dot printing lines to be printed by only normal nozzles. In the opening, a Cr layer forming a plating metal layer and a Cu plated layer are connected to each other. The bracket may include a plurality of ribs spaced from each other and upstanding in a shape of a plate toward the vehicle-body panel such that the outlet is provided between the ribs. The mechanical venting assembly of this invention ensures that the vent openings associated therewith will not become plugged with debris.