Hose barbs with 10-32 threads. It isn't attached directly to the regulator or solenoid. The NV55 is attached to the side of the stand and hose is run to the solenoid on one side and hose attaches it to a CO2 diffuser on the other side. It would be preferable to have an 1/8" NPT connection on both sides or at least the output of the NV55 so it could be attached directly to the solenoid or regulator. According to the engineers it should be possible to tap the bottom of the NV-55 with an NPT port, but the side would have to stay 10-32. With a needle valve, flow direction shouldn't matter. Would it work in your design to mount it using the bottom port if it were NPT?
The first few "trial" pieces will be expensive ($12 - $15 extra) due to the fact they will have to be re-tapped by hand, but if interest is high and the design works out, we can start running batches with this configuration and get the cost down.