Some original thoughts I had was that this could be toy, automobile or bicycle related. There seems to be a great deal of engineering here, and the silver round part spins.
The part that spins could be a guide for material passing along the "whatzit", or the whole "whatzit" itself moving along something that it stationary.
Possibly a guide for attaching grommets or some other fastener to heavy fabric or leather?
I wonder if those two small holes on the top part are for attaching different dies?
Unclemac, you may have solved it. I will take it to my local bike shop. I found it in a city lot that was used as a common play area over the years. I have found auto parts, plumbing parts, and some really strange things there.