I have an old-school brake line flaring tool that I've reluctantly used what seems like 1,001 times to flare 3/16 steel brake line. It's the inexpensive one available at the parts store with the wing ...

Rigid steel tubing with flare and inverted flare fittings is the form of plumbing used on most vehicles. Fuel lines, brake lines, automatic transmission cooler lines and even some air-conditioning ...