It's part of a home-made lab apparatus. Who knows where the one plain rod actually came from - could be lab supply stuff or could be from a metal supply shop.
Remember the stands in Chemistry lab? A vertical rod in a base that you could attach clamps and rings and such to. Well this one was from a soybean oil processing plant lab, used to distill the solvent off oil extracts to measure the amount of oil. It has two different rods, mounted onto a 3-ft piece of 2x12. One with a round base that's screwed into the wood - clearly from a lab supply house - and the other was just a rod pressed into a hole in the wood - that's the one I want to put threads on. I want to make a new wood base for the whole thing so it can be disassembled for storage, because it's quite cumbersome all assembled. Thought I'd embed a nut or two into the wood and put threads on the rod, and voila, easy disassembly.
I don't want to use threaded rod because you don't get a very good surface to clamp things onto.
BTW I'm not using it to test soybean oil. Theoretically, it would make a highly accurate and precise distiller for refining crude distillates of grape fermentation products (and similar materials).