Duster master cylinder fitting size

The nuts in the car are not "standard." There is only one "standard" flare fitting for 3/16 line. All manufacturers did this, and it's to keep assembly line people and mechanics from mis-plumbing the lines.

It used to be a "big mess" back in the days of hydraulic operated trailer brake controllers. I'd guess we used to stock at least 8 different adapter tees to try and cover it. Some nuts are same diameter, but different thread pitch.

Only thing I know for certain is hit a junk yard or cut your existing lines and chance re-flaring them.

"Some" place some suppliers used to sell up/ down adapters from one size to the next