Yeah, this is what everyone has agreed upon
This is the next idea, however there were a couple of bumps. The size of steel rod is so small that I would have to do some research. We called a few of the big steel companies from google searching that specialize is "smaller orders" and it's not a common size so it's a special order which would require a large order. Also the steel rods would not come coated. I would have to coat them myself. Also, the amount of space is so small (as you pointed out) that the nut would have to be TINY and effective... This can all be done, but costly and timely... but I will go this route if the first idea doesnt work (welding 2 nails together)...What i would do is get a steel rod of the same diameter and cut threads into the outside of each end so you can put a nut on as a stopper. That way there are no threads under the plastic and you have the maximum diameter possible.