It's not NPT, it's a straight pitch with an o-ring seal( but I can't remamber the size right now, mabye it's 3/8-24 but not positive)..... I have seen people screw an 1/8" npt fitting into them though.....

I always use the factory inverted flare adaptors with the o-ring and a 5/16 inverted flare to -6 and to adapt to braided line.....