I still don't know what these were intended for. But after having several in my junk bin for years, I finally found a use for two of them.
I have a platform that I carry on loader forks, or on the 3-point forks I built for my tractor. I use lightweight chains to secure loads onto the platform.
I removed the cables from two of those mystery objects then mounted them on the platform's backstop, Now I have something to attach those chains to. The chains are just to keep things from bouncing off the platform going over rough ground, not a high stress application. Now what to do with the remaining ones? Oh well at least I finally found an application for some of them.