The stock spool holder wears down the cardboard on the filament spools, leaving cardboard dust everywhere. I didn't notice at first, but it became obvious on subsequent spools. 

This acts like a simple bearing to reduce the friction on the inside of cardboard spools.

The outside is a cylinder with raised lips on either end to hold the spool in place, and there are ribs inside to reduce the surface area in contact with the spool holder. 

The part can be printed without supports. 

Printed in PLA+ with 5% infill.  

Additional notes:

1. The number and/or the thickness of the ribs could be reduced to further decrease friction. Currently the spool still rotates independently of the part a little bit - it seems that friction could be further reduced with out the risk of unspooling too quickly.
   • Increasing the roughness with the fuzzy skin settings in the splicer could accomplish this as well. 
2. Material could be saved by making the part to fit a 1kg roll of filament instead of to fit the entire holder. 
3. I definitely could have gotten away with thinner walls.
4. I tried to use the SV06 model found here for measurements, since I'm continually losing trust in my cheap aliexpress caliper. When I imported the mesh into F3D and tried to convert it into a parametric model, it just became of mess of triangles. Is this just the nature of the .stl file format or am I doing something wrong?
5. I noticed someone else had the same idea and posted one as well. Sorry about that - I didn't know until I was trying to write this description and wanted to see how similar posts did theirs.