I've got some 26 AWG PTFE wires, and even the small spool looked like overkill. So, I've remixed it to be 12 mm in width (the original spool is 36 mm, and the small one is 18 mm) to fit three spools in one Gridfinity.

Use spoolsmal_b from the original model as a second part.

In the last photo on the left is this remix with 10 m of 26 AWG PTFE wire, and on the right is the original small spool.

I wanted to make it even narrower, but there was no CAD in the original model, and it was too much to edit in Blender.

If you struggle to fix the wires in the corner piece try to put them in opposite order like on the second photo. I'm still thinking about other corner piece design that will hold securely three wires independently.

Note: The middle spool won't be accessible with the power tool adapter. Unwind with care :)