nVent Schroff, PIU COVER WP 21HP 227D, Frame Type Plug-In Unit Cover Plate, With Perforation, 21 HP, 227 mm, Cover plate for frame-type plug-in units, with perforation., Air flow rate in perforated area approx. 65 %, Cover plate is inserted top and bottom between the side Panels, PCB only possible in slot 1