After all three of my Autohelm St4000 wheel spoke clamps cracked, I could not find a source for replacements. I was able to get replacements produced via 3D printing. The new clamps are nearly identical to the originals and are made of black nylon. While the St4000 clamps come in multiple sizes, the ones I had made are the nominal 1/2 inch size.
If folks out there are interested, I can have additional ones made.
Roland Gendreau
Bristol, RI