Simple valve extender for a Presta valve, adds 25mm to the existing valve which should be enough to get a pump on it.
I wouldn't suggest using this as a valve extender under deep section rims, it's good for inflating a tire quickly when there isn't enough valve exposed to get a good connection with the pump head. In my prototypes, it works to inflate the tire, but it does seem to leak a bit, I'd hate to rely on this when the valve is hidden inside deep section rims. If you are braver than I and need it longer, I've included the Fusion 360 F3D file so you can update the height.
It's also designed to work best with a printer that has a 0.4mm print head. I suggest using a 0.100mm (100 micron) print height to get the best results on the threads.
Update: I really mean it when I say don't use it in deep section rims. I had it on a short valve and tried to use it with a floor pump to air up the tire, and it broke off. Luckily, there was just enough of the valve sticking out that I was still able to add some air to the tire. If it breaks off while it's inside a deep section rim, you're more or less outta luck.