I brought this home from the swap meet because it was an odd looking little wrench that had no markings.
Turns out it is a bicycle hub wrench for specific New Departure bicycle hubs.
For a production era, I found a WorthPoint advert on one of these that said: "
For the rear hub on "New Departure" bicycles dating from about 1910 to 1929. “ - I know that's not a definitive answer, but it seemed to roughly agree with other info I found, and since I'm not a bike wrench connoisseur that's a good enough timeline for me.
Wrench is 5.6 inches long. Open end is 5/8" and the inside-to-inside distance between the pins is 1.5” which surround a 7/8" diameter hole.
(The guy at the swap meet had bigger fish to fry. I asked him if he knew what this was for and he said he had no idea. When I asked him how much he wanted for the little guy, that was an orphan among all his other big farm wrenches and parts, he said: "
You can just walk off with it and I won't care."

I flipped him a dollar and thanked him.