a gridfinity module for Marco Bresson's open source cable organiser/winder (small) Holds 4 spools, holds them standing even when not full https://www.printables.com/model/601730-parametric-stackable-cable-organizer-winder-one-wa
2x2 squares 6mm x 2mm magnet holes
update:
2x3 model for the large cable spools uploaded
The author marked this model as their own original creation.