This probably could have been used in a number of ways, but it has the look of perhaps something very specific. The wedge thing may have been used to draw the bolt up against the piece of wood it passed through. Found near the site of a nineteenth century blacksmith shop.
Seems very possible it was the pivot point of a hinge, but I'm not sure about the fireplace crane. This particular blacksmith shop was not a retail establishment. Its purpose was to support a sawmill and its logging operations. The area where I believe the forge stood is now a pile of rocks -- no sign of any bricks there, or anywhere else on the property.
I did find an iron rod within about 10 feet from where I found this item. The rod is threaded at one end, and would fit nicely in the eye of the bolt. Here's a shot of the rod after soaking in vinegar and a little brushing. Its diameter is 5/8" and it length is 7 5/8".