It is a variation on a regular open ended wrench. On a regular open
ended wrench you make contact with the nut on only 2 of the faces. A
flare nut wrench contacts 4 full faces and parts of the remaining 2
faces of the nut. When working on brake lines fittings, a flare nut
wrench is an absolute necessity. The fittings are fairly soft and a
normal open ended wrench *will* distort the fittings. I learned this
the hard way, shame on me
See http://www.redhummer.com/myhummer/tools/wrenches/flarenut.jpg for
photo of flare nut wrench.