which line? Steel or rubber? I have had to make every steel line from the master cylinder out on a '00 2wd a couple of years ago, cut, bend and flare. I have done this job on many vehicles over the years. I can see it coming for my '96 Dakota 4X4 before long.
there aren't many vehicles on the road where the steel brake lines are anything but 3/16". some of the 70s full size trucks and vans had 1/4" from front to back but not since... yeah when I did that guy's '00 it was 3/16.
I reuse the old fittings, sometimes you gotta run a drill bit thru them to get the remnants of old line from them, I'd use a 3/16 bit... many of the fittings have a different thread size than a "standard" parts store length of line will come with, and I don't like to piggyback adapters. more joints = more chances for leaks. I cut, bend and flare all my own lines.