-AN fittings size for trans coolers

[GregWeld]

No "right answer" to that -- because it depends...

Depends on what your female is.... and nobody can see that from your pictures - and even then we'd be guessing. If you have a inverted flare then it's going to take an inverted flare fitting -- not a NPT fitting.

Most likely your radiator trans cooler takes a 5/16" HARD LINE... with a 45* double inverted flare... so if you're going to try to convert that to a -6 AN - you're going to have to figure out what it SHOULD take and then try to find a conversion fitting.