Model D0110DOW, D0110GOW, D0120GOW are "out of wall or floor" integral sleeve dynamic curtain type fire dampers. Model D0110GOW and D0120GOW are designed for supply or return ducts that terminate at a grille or register. Model D0110DOW is designed for through penetrations (ductwork connected to both sides) where the damper cannot be installed within the plane of the wall. UL approved for use where local building codes require the protection of HVAC ductwork penetrations in walls, partitions or floors that have a fire resistance rating of up to 2 hours. These dampers are particularly suited for use in common steel stud drywall partition designs as narrow as 3 1/2" (89), where a traditional "within the plane of the wall" fire damper installation is not possible.