FireRock 42" Cast Iron DamperMade to seal chimneys when fires are out so the cold air doesnt come in, this important element of a high functioning fireplace comes in three different types: cast iron, top seal, and anchor plate with damper. Important to note about our dampers is: Cast Iron Dampers can be used for all fireboxes with the exception of our 72 conventional, which requires two top seal dampers; and our See Through models, regardless if using masonry or metal flue. Top