Okay, so I have an update on the "brass valve":
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I had long been considering the possibility that it wasn't a Presta/Schrader Valve Adapter. It seems like too many of the prequel saber parts are aerospace related, so I thought I would look in that realm. thd9791 and I had been bouncing some ideas off each other when I stumbled upon the Parker Hannifin Model #20-6 "3/8 in. x 1/4 in. Barb Brass Plug". This is a simple plug used to plug the ends of open pneumatic flexible hoses:
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The sizing looked correct, the knurling looks perfect, the only problem was the stem and the fact that the inner diameter wasn't threaded. Anyways I picked a few up, and after 10 minutes of easy modification I'm pretty happy with the results. All it took was cutting down the stem with a hack saw, and tapping the ID with (in this case) an M6 tap.
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I'm not saying this is exactly what was used, but it's a possibility, and a good option readily available for cheap:
Order Parker 3/8" x 1/4" Barb Brass Plug, 20-6 at Zoro.com. Great prices & free shipping on orders over $50 when you sign in or sign up for an account.www.zoro.com
Great find. I think you just figured it out. This type of part, previously unknown to me, is a much stronger candidate than the bike valve. The barb knurling does look perfect. The fact that it also has that extra step around the top face is a strong indicator. I like your idea about the stem being cut short and how that matches with the small set screw mount seen on that stunt saber.
The version you found does differ in some dimensions from the prop, but it's such a close match overall, that it would be odd if it weren't the correct type of part.
The trick is finding tooling to reproduce that knurling... it's close to a 45 degree knurl, but not quite... I looked around on MSC for a bit but couldn't find anything correct.
What do you think about shortening the barb knurled area from the stem side? What does the bottom of the valve look like in your high res reference photos? Does it look like it was lathed short, or do you think that the original part was just made shorter 25 years ago?