All the Gridfinity wire holders I could find were for vertical spools in drawers. I wanted something that would allow the wire to lay flat in a case like the rugged case. There are two versions of this model, one is stackable, one not. The design is intended to fit flat in a 4U of gridfinity space. The circles in the base are so that the wire end has a space to goto. 

The 78mm diameter wire spool I made using the Customizable Wire Spools openscad model.

Printed on a Bambu P1S using Bambulabs PLA Basic.