I liked Tomrms design but I didn't like the gap always being open. I wanted something quick and easy to add and remove the filament.

There is a long model and a shorter one.

For the spring I used a standard paper clip straightened out with no bends or kinks, then tightly wraped tight around a 6.5mm drill shaft. Look at the example spring so you wind it the correct direction. Clip off so it fits into pivot asm.

You can saw off the rear tang leaving 10mm of support in case you have something blocking the rear opening on the top 20x20 bar. There is also a support block if you feel you need it.

Clear out the hole in the pivot with a 3mm drill. I taped the hole in the main guide 3mm.
Use a 3mm screw and nut . I superglued the nut to the screw after assembly.

I hope you like it as much as my kitty.