Master cylinder brake line replacement

It would help if you volunteered the year and model of your car. My 64 & 65 single-pot MC's had a 1/4" tube w/ double-flare. The matching fitting on the MC and splitter block is termed "1/4" female inverted flare".

This would be an opportune time to change to the much safer dual reservoir MC. Many have done so. I went power booster on my 65 Dart and am converting my 64 Valiant to manual, both newer aluminum MC's. To do this, get a "1/4 M to 3/16 F inverted flare adapter" for the top port of the splitter block and a "3/16 inverted flare plug" for the rear port. Also get a 3/16 inverted flare coupler to attach to your existing rear brake tube.