Why doesnt it exist when so many DIY projects now use PET bottles? That's a very good question and just off the top of my head. One could take a cap from each and glue them together back to back and mount them in tubing then drill the center out. Or if you have the equipment to machine a adapter fr...

Or long gone? Looks like it. What pressures are you looking to run at? Using it for a non gun purpose where I MUST HAVE "Screw on and off" capability while holding water without leaks. The 3D prints seem a a bit tough due to 3DHub saying PLA prints might have issues with threads. Might have to go f...

Thanks for responding. Yes, I did find the 3D print models; currently looking at local 3D prints that may be affordable in material/ strenght I want.

I was wondering if there are any of those old types available or made by anyone? Or long gone?

You can buy an adaptor for the typical soda bottle thread from Spudcom.com , Two-Liter Pop Manifold [P-500] I know this is old, but is there any such thing available on the market now? Need something thats easy screw on and off between NTP/ NPT (US) and / or BSP (UK) Standard Pipe threads AND typic...