1965-67 Chevy Oil Pressure Guage

Looking for the fitting that screws into the back of the factory oil pressure guage for the years 65-67 Elcamino or Chevelle. It appears to be smaller than a 1/8 inch and is pipe thread. Any thoughts would be appreciated

Any decent hardware store should have a box of brass pipe fittings, usually behind the counter. My local True Value and Ace both have great assortments, or try any good auto parts store.

Bob