I'm not sure of the current price for a fill stem from Hypertek, but here is a home made one made by Butch Hanna of the Albuquerque Rocket Society. This doesn't go into depth of the parts, but a printout of this page taken to a business that knows fittings and they'd look at it and say "oh that's a ...".
The tubing is actually brake line. The center fill stem should be filed down to smooth it at the end so it doesn't tear up the O-rings in the Kline valve. Note that if you use a tank that has a ball in it to disperse the nitrous, you either need to do something fancier with the end of the fill tube (Hypertek's come to a 'merged point with holes around it' - find one and look at it) or else simply insert the fill stem while the rocket is horizontal so the ball has already fallen out of the way.
Anyway, here's the complete item. (The Albuquerque Rocket Society - ARS - uses quick disconnects for the GOX and Nitrous - hence the air compressor (for GOX) and hydraulic (for Nitrous) fittings below. You could use regular screw on fittings and save cost, but changing between motor sizes wouldn't be as easy.1
Here's a closer up pic of the top; Note the outer tube laying separate (the GOX tube) slides over the other fill tube.
Here's a closer up pic of the bottom; note the T had to be drilled out a bit so that the 1/4" brake line fit up through the middle. The GOX comes in from the T and flows around the fill tube. With this setup, you could probably use one 'base set' of hardward and simply swap out the fill stem and GOX stem with different lengths for the different motor sizes. Most of the more expensive fittings would be re-used across the three different motors.
Here's a reasonable close up of the main pieces; this covers all the actual fittings and brake line. Note again that the ARS uses quick disconnects for both the GOX and the Nitrous.
- 1/4" brake line tubing (Checker Auto Parts)
- 3/8" brake line tubing (Checker Auto Parts)
- If you get the above tubing long enough, you can make both a J and L fill stem
- For the L Bell, you'll need to insert the fill stem while the rocket is horizontal so the 'ball in the bell' is out of the way. (Hypertek fill stems are pointed so that the ball falls out of the way.) If you don't understand what I'm saying here, look at the L Bell.
- 1/4" MPT to 3/8" Flare fitting with Nut
- 1/4" FPT "T" connector
- 1/4" MPT to 1/4" FPT 90 degrees elbow
- 1/4" MPT to 1/4" MPT nipple (times 2)