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-set inserts goes in the end of the spool holder arm to clamp the 1/4" steel rod; you might not need it; you could glue it in just fine.

The other goes in the clamshell; you might be able to substitute an M5 nut, but I used a brass m3 heat set insert that's 3mm long and 5mm wide. (I bought an assortment on Amazon, and I highly recommend them to anyone who's 3d printing stuff they wanna screw together!).

The thumbscrew on the clamp also has a heat-set insert in it. I will probably make one wi