Unusual antique casters

Hi, I was wondering if anyone out there has ever seen this unusual type of furniture caster. I just purchased an all original platform rocker that’s been in the same family since new. I noticed that the base was loose and in need of re-gluing, so I proceeded to disassemble it. That’s when I discovered the interesting casters it has! It took me a bit to finally discover how to remove them: they are threaded in. But once removed, I realized just how odd they are: I’ve never seen anything like them before, but May someone out there has. Each wood wheel is attached to a cast iron swivel, which is enclosed by separating halves that, once joined, are threaded. They thread snugly into the bottom of the leg, and have flat spots so they can be tightened with a wrench! No marking except “PAT’D” as well as the number 4 on each swivel. If anyone is familiar with these and can help date them, I’d be grateful.

 

Here are some better pictures!