Bending and flaring brake/cooling lines
In the 20+ years I spent behind the parts counter at my familys parts store, we used a KD brand flaring tool and a KD tubing bender. The flares on any of the domestic automotive stuff during the 70s and 80s that I dealt with on fuel, trans cooler, and brakes were inverted flare (I guess now they call it double flare?) The inverted flare tool had inserts that fit into the end of the tube (one insert for each size tubing). The forcing cone of the flare tool fit into a dimple in the insert to keep it centered. The handle was screwed in till the insert was forced down and the tube was bulged out like a mushroom with the end retaining it's original i.d.. The insert was removed and the handle screwed down again with the forcing cone shaping the inside of the tubing into a flare with what was the outer end of the tube now on the inside, and flared out. Cheap flaring tools (two bars with holes held together by wing nuts) just don't work from what I've seen, and I've never seen one do an inverted flare properly. The KD flare tool had rotating dies that were changable for 3/16" - 3/8". Not sure if they are still selling the same tool now....