well like the two previous posts mentioned, the nut for the fitting is a softer alloy. so to grip all corners (so not round off the corners) you'd want a box end wrench. But since a box end would not allow you to remove after its tight(because it would have a brake line inside it). so there is a flared end wrench that has a slit in it large enough to allow the brake line to pass.
strip that fitting and you have to cut the line, get a new fitting and then flare the line (with a flare tool) to get it back. big hassle for stripping it
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