From one who has been there forget the double flaring UNLESS you have a nice hydralic type
Hydraulic flaring tool. Yes, they are very nice. I don't even use the old style anymore, last time I used it was to make the flaring video. The hydraulic one is faster, easier, and makes better quality flares. The set I have (mine came from Snap-On) also does ISO "bubble" flares found on most late models, as well as the push connect (GM and Ford style) fittings. I don't have the dies for them, but there is also a kit for doung the 37 degree flars, too.