I noticed all the pieces are hand fabricated. Cut and bent, filed into shape. A specific use in mind, but what? I think they're adjustable wall mounts for something. The larger part of each that is bent, with the side flaps, would be mounted to the wall ( probably vertically ), with the fat nut and bolt already in place. The protruding bolt in front would be placed through whatever you're hanging, the item leveled, then the large thin nut would tighten that down. The side flaps keep the rear nut from turning. If these units were found assembled, then whatever was mounted was probably wood, long gone. If these haven't been fiddled with, if you pull thin nut and bolt end, drawing the fat nut tight into the slot, measure the gap between the thin nut, and the wall mount, and you'll know the thickness of the wood that was mounted.