You need 2x per roller axis. They are meant to be press-fit. If you put them on the outermost of each axis you are able to use spools up to Prusament spools (are my widest).

Hint: The sleeves are for the bigger-spool-inserts :) In the comments I got the information that you need to scale it down to 70% in diameter to use the sleevees with the smaller ones. (Not tested by myself)

Improvements:

• Spools moves better instead of scratching over the plastic.
• Reduces noise.

Print:

• Print with TPU (I've used ERYONE TPU 95A)
• .15 or .20 layer thickness
• No support needed ;)

Please see my other models used for my drybox based on a IKEA Samla box: https://www.printables.com/@Mike_88377/collections/1315141