This is the cast iron fire fence or log retaining bar that sits at the very front of the Mulberry Beckett firebox. This part plays a very important role of keeping fuel from falling out of the firebox when you are refueling the stove. Over time, as with any consumable part on a stove, this part can warp with it being subjected to continuous heat and should be replaced. This will help keep you safe in using and refueling the stove.
