For nearly any car, you need these things. This is not "special", but many people still ask, "What's a flare nut wrench?" As in the picture below, it looks like a box end wrench, except with a small section of the end removed so it can be slipped over a hose or tube for use on those pesky tubing end fittings called flare nuts. The flare nut wrench will always be six-sided (with one side missing) and thick wall for rigidity. In use it will catch 5 corners of a 6 corner nut and allow high torque without ripping the corners off of the nut or collapsing a thin wall nut like a two-sided open end wrench would do. This is especially important for tubing flare nuts which are thin wall and subject to being easily smashed, and for brake line fittings which are small and easy to round off the corners.

Pictures here show a few of the many uses for this handy tool.

Temperature sensor, hollow nut, male thread.

Brake line flare nut, small hex, male thread.

Fuel hose flare nut, thin wall, female thread.

For that (hopefully rare) occasion when you truely butcher a hex nut fitting and round off all the corners beyond any hope of getting a grip with any normal wrench, even a flare nut wrench, here is a solution that could save your britches. You will have to sacrifice a good wrench (make it a cheap one), but it may be the only way out of a jam. Starting with a 12-point thin wall box end wrench, cut a narrow notch out of the end to break the ring. This will destroy the normal function of a box end wrench, because it will lose a lot of rigidity with the ring cut open. Slip this seemingly worthless tool over the damaged hex fitting, then clamp a small locking plier onto the ring of the tool to constrict the metal onto the damaged fitting for a good grip. This way you can get a really tight grip on a hex fitting without smashing it, even when there are no visible corners left on the fitting.

Getting a grip on a rounded flare nut or brake bleeder nipple.
Sacrifice a cheap box wrench.