What size(s) you need depend on what flare-nut(s) you're trying to work with. The application determines the tool needed.
I frequently crack the nut loose with VISEGRIPS
Flare nuts are typically thin-wall, mild steel. A vice-grip merely distorts/crushes the nut, causing it to drag on the tubing. Using a vice-grip instead of a flare-nut wrench/crowfoot is asking for trouble. If a vice-grip seems viable, you need better flare-nut wrenches.
I wonder if the "line" wrenches that you all are refering to are what I know as "tubing" wrenches?
I'd have called them "Flare-nut wrenches". "Lines" are imaginary objects. What you're dealing with is not a "line", it's
tubing with a flare on the end, held in place with a
flare nut.
My biggest issue today isn't with rounding the nut off it's with the nut being corroded to the brake line. I deal with this on Dodge Trucks a lot where I brake the nut loose then notice the hard line is flexing with the nut. I try soaking them in oil and everything and nothing ever seems to work!
Oxy-Acetylene to the rescue. Potentially you could use one of the portable inductive heaters. The main problem I've experienced with heat on flare-nuts is when the flare-nut is what's connecting brake tubing to a brake hose. The hose is very likely to pop free of it's crimped fitting when the flare-nut is heated.
Mac USA are every bit as good (and even slightly better according to TTC's testing). Having metrics in Snap On and SAE in Mac, both are every bit as good as each other.
The single MAC USA COBR13MM flare-nut wrench I have is a thin-walled, flexy piece of ****. They weren't in the MAC catalog long.
Shorter length is rarely useful, more-often a detriment.
Lack of angled head is similarly a detriment most of the time.
Assorted scrap metal. 12-point flare nut wrenches may be useful in Aviation. They are a bad joke in automotive use. Thin wall-thickness makes a flexy, slipping wrench. Short lengths trade away leverage
and control. The Craftsman and the NAPA units are the "best of the worst".
Potentially the worst-design of flare-nut wrenches are those that only have four "corners" to grip the flare nut. I first saw this on Hazzard-Fraught junk "tools"; but since then I've seen it on Proto, Urrea, and Sunex, and perhaps other brands.
A proper flare-nut wrench grips five out of six corners on the flare nut.
Four out of six is just silly.
