I started buying stranded wire from Amazon, cutting the sheathing and separating out the colors. I found this to be less expensive than buying separate colors or even color sets often. These spools work great for re-spooling.
These fit together like a glove so I recommend giving the inner shaft a tiny sanding before assembly, like one or two spins. If need be you can tap them together with a small hammer. lightly tapping the center. It's a great design just wanted thicker walls and gave better information as to gauge and length the spool will hold.
The author remixed this model.
Thickened the sides another 1.0 mm