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The tube is a micro piece of SS hard line (0.05" OD) that you can get from McMaster, and is brazed to the inside of the custom fitting. This joint actually wasn't that hard to braze – you can put flux and filler metal into the larger hole on the inside of the died 1/8 NPT side. Then, you can slide the tube inside and heat up the fitting from the outside with a propane torch. IMPORTANT: In the CAD photo, the needle tube is only barely sticking out above the surface of the fitting on the inside; this is supposed to be mOsT oPtiMaL but in reality it needs to stick way above that to allow the flux to sit below and not clog the inside of the needle. Once the fitting gets to a rose red, the joint has probably heated up enough on the inside to melt the flux and seal it. Example below!
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