Well we noticed this really old thread and see that it still gets lots of hits on Google. So if anyone is still looking...

Gary: "But I can't figure out what the thread size is on the R134a. Please
enlighten me!"

I grabbed a bolt and checked if it screws in to the R134a in or out. It fits.

1/4" - 24

Meaning a 1/4" diameter bolt with 24 threads per inch (fine thread)

Someone should confirm this.... but does that help anyone?