Help identifying an odd fitting

[Sorefoot]

Can someone help me identify this fitting? It’s on a 93 Saturn that came from the factory with R12 but it appears someone did a conversion. My low side coupler snaps into place easily and when I first saw the threads on the outside of this I though maybe they hadn’t converted the high side fitting for some reason. There is also internal threads but my coupler won’t lock over the fitting. No sticker anywhere saying it’s been converted but I’m starting to assume it was.

Also, I borrowed a friends set of R12 gauges and they won’t screw on to the threads either.

Thank you.

8A69C86E-331F-4331-86E9-03314106A56D.jpeg (69.41 KiB) Viewed 4337 times

[GM Tech]

Under that adapter is the original R-12 fitting--they only did the low side adapter--some folks are lazy....

[Sorefoot]

Thanks. I guess I should have said specifically I was asking about the high side.

I think I figured out last night that GM used a weird high side fitting on cars from 91-93/94 right before they switched to R134. I'm guessing whoever had the car before bought a conversion kit and the high side fitting wouldn't fit (because it's this weird GM thing) so they just threw the low side on and filled it with 134. I read somewhere the GM did this because they knew people would be doing these conversions and they wanted to make sure nobody screwed up and put the wrong 134 conversion coupler on the wrong r12 fitting and then tried filling through the high side.

[Cusser]

The gov't made manufacturers use a different size high pressure side R-12 fitting so folks could not readily confuse those. There was a GM-type used by GM and Toyota, and a Ford-type used by Ford and Mazda (including my own 1988 Mazda truck). This happened about late 1980s, and I have both types of R-12 adapters, as my 1988 Suburban needed the GM type.