Not sure those brakeline plyers will work on 5/16" or 3/8"
I just bent up 3/8" trans cooler lines for an O/D trans. I had a cheapie bender that had index marks on the side so you can see the number of degrees your bending the line. I kept collapsing the steel line in the outer radius of a 90° bend with it. I ended up capping the one end with aluminum tape, filling the tube and packing it tight with sandblast sand, capping the other end, and then bending the tube. After which I shook and blew the sand out. Worked fine. Old skool way of mandrel bending.
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