Are you dealing with straight threads or tapered? It would also help if you mentioned a thread diameter. The simplest approach would be to rethread the gauge to an easily-accessible thread. If you don't want to alter the gauge and you have access to a lathe, make your own adapter fitting. Brass threads easily- - - -I love to work with it. Once you get a thread that fits, a few drops of blue Loctite will keep everything assembled and leakproof.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!