Those concentric grooves on your new cylinder's end cap are obviously intended to engage a copper sealing ring that's used with a banjo fitting. I'll bet the threads are straight, intended for a 1/2" or maybe a 9/16" banjo bolt.
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!