Nailor Model 0722 Ceiling Dampers are for use in spherical apps, in lieu of hinged doorway variety dampers in almost any UL/ULC flooring/ceiling or roof/ceiling assembly with approximately a 3 hour hearth resistance rating where air ducts are authorized. Sizes accessible are restricted only from the system design and on-web site Place envelope constraints. https://dampersforindustrialsecto13456.mybuzzblog.com/16904414/heavy-duty-stainless-steel-damper-manufacturers-an-overview