That fitting has a 5/8" straight thread (not tapered pipe) which matches the nut on the mechanical gauge capillary tube and a flat seat for the bulb to seal against. They used to be available at every corner auto parts store. Not any more! 216's and early 235s had that thread in the head and didn't need the adapter.
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!