What size brake line to use?

[95bucket]

I’m upgrading to the NBS master cylinder and all of the rusty brake lines are being replaced also. Should I be using different size lines since I’m putting a newer master cylinder on? Thx for any advice

 

[arrg]

Both fittings on the NBS master are 1/2"x20. Stock on our trucks, the flare fitting to the front brake line is 1/2"x20 but the rear brake line flare fitting is 9/16"x18. Since you're running new lines, you could make that change and avoid using the adapter you'd otherwise need to put in the NBS master.