It's a tool for holding a ham. You unscrew the ring, for it over the bone and tighten it. You now have a long handle for assisting you when carving from the ham joint.
DH father had a grocery shop. He boiled his own hams on the bone in a huge machine in the back room of the shop. They had a tool just like the one in the photo, for carving the ham at home at Christmas. It was in my MiL's kitchen drawer for years.