This adds weight to your spools so they stay in place when there is little filament left.
Tested with many brands of filament spools like Prusa, Raise3d, Sunlu, Eryone, BambuLab, Wanhao, Flsun, Geeetech…
Some spools like Geeetech need “Extender.stl” part to be used because the inner diameter is larger than normal.
It was modeled to be used with a weight of 500g available here: