I've had this casting hanging on my shop wall for ages. The internal diameter of the ring is 5 inches. I assume it's some sort of sling, although it wouldn't bear a lot of weight. As you can see from the photos, one side opens outwards when a wedge pin is released at the top. The internal diameter of the closed ring is 5 inches. The hex shank is internally threaded, so it's clearly meant to be threaded onto something else, probably suspended from above. The only marks are "NEH" and either "CK" or "OK". Curious.