Thank you for your answers. Very useful as always!
I think I have control on the 45 degree double flares and 37 degree AN single flares in my brake system.
It was the 1/8" NPT fitting on the inner connection of the thru frame fitting that worried me a bit.
One more thing.
I'm using a Corvette MC and to make it accept the 3/8" double flare fittings, I had to buy two adapter fittings intended for this purpose.
But one of them seems to not have enough threads? It screws all the way in and I really don't know if it is the flare inside that stops it, or that the threaded area on the adapter fitting simply is too short and stop it that way..?
Any of you with experience on this?