Almost everything before about 1960 was 1/4" lines. After that you start to see some 3/16" appear and with the advent of disk brakes, lots of 3/16" was used with special sized nuts on the master cylinder.
'38 Chevy 1-1/2 ton '49 Chevy 1/2 ton '54 Chevy 6400 2 ton '55.2 GMC 3/4 ton '56 GMC 1-ton
