I was at home depot picking up a needle file set for working on my helmet and walked past these and thought imediately of knee darts. I don't know if these have been found before or not. In the same section (air compressors) there was a piece that looked like a giant bordon connector so maybe the original connectors were used in dental tool air compressors? Just a thought. It's hard to tell in the horrible phone pictures but on the end without the hex there are grooved lines, not threads (spiraled) but parallel grooved lines. Anyways tell me what you think. I turn it over to the experts.