Models 0110DOW, 0120DOW, 0110GOW and 0120GOW are "outside of wall or floor" integral sleeve static curtain form fireplace dampers.  Design 0110GOW and 0120GOW are exclusively suitable for source or return ducts that terminate at a grille or register. Product 0110DOW and 0120DOW are suitable for by means of penetrations (ductwork https://trevorpgviw.blogcudinti.com/37131136/the-definitive-guide-to-heavy-duty-stainless-steel-damper-manufacturers