IMO it's a little small to be a heel plate. I've found some small ones, but the odd shape of this tells me it isn't that. Maybe a musket part? Bottom part of a copper kettle handle (where the handle attaches to the side)?
It clearly had 3 screws which went into wood & was built to take weight or stress. So it could be missing a hook for heavy duty purposes or a broken hinge, maybe even a window fitting
Makes me think of this piece I found that for sure came from a early site.It also had counter sunk screw holes.But are very crude formed.And is purdy thick copper.