What is size of the fittings on our old 1/4 " lines?

Correction to my title. I in fact have 1/4 brake line , not 3/16. Now I think after it hits the distribution block, they turn into 3/16 lines.Getting set to do the drum to disc swap, including new MC, prop valve to rear etc... I am trying to find the right adapters for me to connect new stuff to the old brake lines. Does anyone know the size of the fitting on the line that screws into the old MC? It looks like the line screws into a fitting that screws into the MC. Same at the old proportioning valve. I want a fitting that allows me to connect the new dual MC, to the existing 1/4 line. I;ve read that it might be 7/16x24? But that seems too big? What is the normal fitting for the 1/4 brake lines in the 66 dart with 9 in drums. Also checked manual and no mention. Thanks
I do know that the new MC has 9/16x20 and a 1/2x20 outs. And I am going to run a new line that will have 3/8x24 fittings from new MC to old proportioning valve.