
I also finally assembled the threader using the handle that Beth turned for me:

(I drilled a hole in the end, then covered the wire in epoxy and inserted it; finally I shaped the left-over epoxy into a cone around the wire.)
Also, for those interested in building your own spinning wheel, here's a really easy but very nice tensioner:

The tensioner is just a dowel in a clamp. The handle was chewed by a (bad) dog; I'm making a replacement handle out of a cherry disk, which both looks nicer and offers less purchase for a dog's teeth. For those unfamiliar with how to build a tensioner, the spring doesn't do anything relevant during spinning — it's only purpose is to make it easy to undo the tension cord to remove the bobbin without losing your tension setting.