One of the standard tool-handling exercises in my auto mechanics class is making double flares. All my rookies learn that, plus the right way to do a solder joint on electrical wiring before they can move on to more advanced projects. Besides brake lines, any custom-fabbed air conditioning line or steel gasoline line needs a double flare. Steel lines crack if you try to do a single flare, plus they don't seal properly if you happen to get a flare made without a split.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!