In the pictures you can see one of the fittings that came in a fitting assortment I purchased. Alongside one of the plugs that came with the master cylinder. The plug has a slightly finer thread. 0.54 diamater. I'm trying to work out the thread pitch.
Well geez, if it has a brass flare inside you should be able to screw a double flared line into it as long as the flare nut is the right size. We can't see what you have unless you show us.
