Do you know if the threaded fittings are the same for either 1/4" or 3/16"? Was there a reason why you change to 3/16"?
The threaded fittings on these trucks with the 1/4" hard lines are 7/16" x 24 TPI (Threads Per Inch).
I bought some fittings with the same thread for 3/16" hard lines by mail order from a supplier in PA. Ordinarily, the fittings for 3/16" brake pipework would be 3/8" x 24 TPI.
I used 3/16" pipework because it is so much easier to bend and install. Also 3/16" corrosion resistant Cupro Nickel brake pipe is much easier to get hold of here in the UK than similar 1/4" brake pipe.
I have been told that the reason 1/4" hard lines were originally used was that they would require fewer retaining clips than 3/16" pipework. I used lots of clips along the chassis when I reworked the brakes; I wouldn't want to risk a pipe failure resulting from vibration on any rigid pipework -especially the brakes.
