This is a spindle for 40mm spools.
Combine with some Tinkertoys and you've got yourself a handy way to feed another color into your printer without removing existing spools.
No construction necessary. Print two and fit onto a 1cm shaft.
Depending on your printer's fidelity, you may want to wrap a piece of tape around the inner shaft of each spindle to ensure a snug fit into your spool.
I use a strip of painters' tape on each spindle. Works great.
Seej patient zero. Barbie Armor Designer, artist, worst programmer ever. Mostly illiterate, but has minimal competence in spoken Mandarin. Not real clear on Ohm's law.