Hy Russ_B_10, it would appear that there is an error in most of the brake parts catalogs, I verified this morning by looking at a 1954 1/2 ton chassis that the front brake lines are 3/16". Most of the catalogs list the brake hose as having 7/16"24 internal thread, which is the size for 1/4" brake lines. I crossed the o.e.m. p/n 3696551 for the flex hose at the Napa site and came up with the Napa p/n UP13841, the picture and description shows 3/8 internal thread and the correct horseshoe clip attachment to the bracket on the frame $17++ at Napa. The Raybestos p/n is BH13841 $12.61 at RockAuto. Even though the illustrations show everything to be the same as O.E.M. sometimes when the part arrives it has an external thread at the frame attachment end, which requires a locknut (jam nut) to affix it to the frame. I did go over to the Inline Tube website to check it out, but I couldn't find a way to make any specifications for their flex lines to appear, I hope that helps.
