This piece has me stumped. Do you have any idea what it is?

Looks like a cast-iron structural bracket, perhaps for a buggy or wagon. The two rings would have long bolts through them, on either side of a beam that would snuggly fit between the four lugs at the corners.
Hard to guess what matching hardware would be on the opposite side of the beam, at the other end of the bolts; maybe a cross-piece, or a fitting for some other part of the chassis.
All of this is simple conjecture, of course; it's just the kind of thing I would have picked up...Thanks!