I have started making my own (single action) truss rods. 3/16" steel rod, threaded on one end, bent by heating over a blowtorch, then I bought a bunch of those spoke-wheel nuts from Stew-Mac... I made a brass "sleeve" for the nut to press on. Basically, it is a small brass block with one hole clear through it, and one only *most* of the way through. The threaded part passes through the open hole, and the unthreaded end sits in the "pocket" hole. Works pretty well, and I can do all sorts of custom lengths.