Design D0110DOW, D0120DOW, D0110GOW, D0120GOW are "outside of wall or flooring" integral sleeve dynamic curtain kind fire dampers. Model D0110GOW and D0120GOW are made for source or return ducts that terminate in a grille or register. Design D0110DOW and D0120DOW are designed for via penetrations (ductwork connected to both sides) exactly https://heavydutystainlesssteelda01122.bloguerosa.com/35960184/the-5-second-trick-for-dampers-for-industrial-sector