Model D0110DOW, D0120DOW, D0110GOW, D0120GOW are "out of wall or flooring" integral sleeve dynamic curtain form hearth dampers. Design D0110GOW and D0120GOW are made for supply or return ducts that terminate in a grille or sign up. Design D0110DOW and D0120DOW are created for by penetrations (ductwork linked to both sides) https://dampers-for-industrial-se70022.webdesign96.com/37329673/5-simple-statements-about-dampers-for-industrial-sector-explained