Nailor Product 0722 Ceiling Dampers are for use in spherical programs, in lieu of hinged door kind dampers in almost any UL/ULC ground/ceiling or roof/ceiling assembly with up to a three hour hearth resistance ranking wherever air ducts are permitted. Styles 0110DOW, 0120DOW, 0110GOW and 0120GOW are "outside of wall or floor" integral sleeve https://dampersforindustrialsecto80122.blogsmine.com/37433563/not-known-details-about-dampers-for-industrial-sector