3/4" NPT is a massive entry for a solenoid valve. If the entry is about 2/4" diameter then it's probably 1/2" NPT.
Are you tied to Hirschmann? Which series of connector? The commercialised military types I referenced above are fairly popular for things like solenoids, servo-valves and the like in power generation, steel, those sort of environments. Not much use for hazardous areas, but excellent otherwise. You might find the beautifully-engineered Hirschmann or Lemo type connectors don't like the rough & tumble in an industrial facility, if that's where your valve is located.