Spool Holder for i3 Acrylic Frame

I borrowed the end "box" from https://www.myminifactory.com/object/3d-print-8mm-frame-filament-spool-holder-29092 and merged it in Meshmixer with the original arm (which is designed to accept a wide plastic tube). My arm is otherwise identical but accepts a 1/4" threaded rod. As the fellow at myminifactory suggests, consider printing this spool insert http://www.thingiverse.com/thing:767317 to go along with this item.

Update Oct 2021: I added another version with a "stabilizer plate" to