Hey Denny I am pretty sure that I have seen in more than one tech article that the reason for not double flaring stainless is that yes it work hardens and even a good looking flare is likely to crack in time with use.
I worked in aviation hydraulics for a number of years both military and civilian and all those AN flared fittings on stainless are single flare and some of the systems ran as high as 6000 psi. I don’t know a lot about the fittings used in automotive brake systems but the tech articles that I seen where dealing with automotive brakes. I just don’t remember where I seen them. I will post this as a question for Stacey David on his web sit. I am sure that it came up on one of his old shows. I don’t know how long it will take him to respond he doesn’t seem to be around much.
