These are really interesting. I bought a few from a rowp a few years ago, and found I had three different iterations of them. The early ones have the eye firewelded to the spring, later ones have a one-piece stamped spring and eye (which is what I think yourself may be), and the later 1950's versions had a wire spring. You should find a makers name stamped on it somewhere? Hanes were very prolific.
Rightly outlawed since the later 50's, but they're a very interesting piece of agricultural history I think.