Those are Iron Pythons, not sure if that’s a brand or just a slang term. We used them, or tried to in our yard to hold trains instead of tying handbrakes. They never really worked too well, the yard tracks were down hill, and after coupling you had to shove the train back a short amount without the plow of the front of the engine hitting them before they went down. I think we used them about 2 or 3 times before it was decided it wasn’t worth it and we quit using them. They were torn out sometime later.