There are a wide range of flare nuts out there for heavy machinery, diesels, and many other industrial needs.
In turn, flare wrenches are designed to fit this wide range of flare nuts. Whats unbelievably frustrating is the frequency for which brake line flare nuts get stripped even while using those ‘flare wrenches’.
European tool makers however make brake line specific flare wrenches; the difference? Brake line specific flare wrenches are thicker and gusseted; both reduce the tendency of the open end to spread, grip the nut more wholly, and prevent the wrench from slipping off.
Example Hazet 612N series: