Nailor Design 0722 Ceiling Dampers are for use in spherical purposes, in lieu of hinged door variety dampers in almost any UL/ULC floor/ceiling or roof/ceiling assembly with up to a three hour hearth resistance rating where by air ducts are permitted. Wall and roof-mounted dampers are applied to mechanical HVAC air flow units. Generally https://dampers-for-industrial-se01222.digitollblog.com/36679308/heavy-duty-stainless-steel-damper-manufacturers-no-further-a-mystery