this is a really informative post,
with information that is almost impossible to find elsewhere on the internet.
I know, I tried, and posted a question asking for the information,, without sucess.
Eventually, after quite a time I managed to clean up the hexagons of my old brake-line nuts
to a point where I felt happy that they'd be 'up to' the important job they have to do.
Getting the correct brake line nuts is vital for safety,
using 'something-similar' that threads on,, is just NOT SAFE.
So, well done, Chevychase for finding and sharing this information with us.