Someone else could chime in if they know for SURE, but most of the trucks I have seen have 1/4" lines with 7/16 ends throughout. The stainless kit I got from the vendors was all 1/4" except for the one piece that runs across the differential.
I am not a hydraulics engineer so I don't know the true ramifications of using smaller line. Wish I did. The proportioning valve in this front disc brake kit has 3/16 (3/8") fittings and so does the rubber hoses to the calipers. I had to use an adapter at the prop valve to keep my 1/4" lines and two more at the rubber hoses. Testing the system today, works really nice the way it is, but is this okay? No idea! I chose to NOT use a booster but it really feels like all four corners are working very nicely.
