Yet Another Railcore 2 Spool Holder

So @chainsol made a one-arm remix of my two-armed quick-n-dirty spool holder, and it gave me a couple of ideas, and I can't leave ANYTHING alone, so here's my remix of his remix etc. :D

This has a screw in the top surface to clamp to the extrusion. It uses two brass heat-set inserts. You might be able to get away without either one.

There is a part that isn't printed; this is designed for 1/4" steel rod as the spool carrier. ( 6mm will work if you're not in the USA :D ). One of the heat-se