I built a 36" steel UW out of scrap parts for @Setonix where I created a “crank length selection bar” and didn’t have the correct pre-drill.
So I used hemp fiber, like used in water installations. It was a nice tight fit which didn’t get loose. Hemp fiber and @Setonix’ PTFE band are used in water installations, where hemp fiber is more forgiving for small corrections in screw tightness.
Later I built my own aluminium 36" UW.
