Types 0110DOW, 0120DOW, 0110GOW and 0120GOW are "outside of wall or floor" integral sleeve static curtain variety fireplace dampers.  Model 0110GOW and 0120GOW are exclusively suitable for supply or return ducts that terminate at a grille or sign-up. Product 0110DOW and 0120DOW are suitable for by means of penetrations (ductwork https://cesarjzper.thezenweb.com/the-definitive-guide-to-dampers-for-industrial-sector-75222987