This is remix of Sisul's modular wire spool holder, as well as zmadmani's model on Thingiverse which is where I saw it first.  My main goal was to make connecting the individual modules together a little easier and, instead having just a V notch for the wire, I wanted a hole that the wire could be threaded through to keep it somewhat captivated.  I also added a hole in the bottom of the modules, to make it easier to get spools out of each module.  You can simply press a screwdriver or any small diameter long object through that hole to help push out any one of the wire spools.

My design consists of 5 different parts as follows:

1. Main Body - Right (used as the module on the far right side of ganged modules)
2. Main Body - Left (used as the module on the far left side of ganged modules)
3. Main Body - Inner (used as the module(s) between the Right Side Module and Left Side Module of ganged modules)
4. Left Side Cover (used as the cover for the Left Side Module)
5. The ReelCenteringUnit.stl from this Thingiverse model.  You can also use the ReelCore.stl and ReelDisk.stl from that same model, if you need empty spools.

Each module connects together with two M3x6 socket head cap screws, one on the bottom corner and one on the back top corner (see photos).  The Left Side Cover attaches to the Left Side Module using three of those same screws.

No supports are needed to print any of the parts if printed in the optimal orientation.

[UPDATE 2/13/2024]

Modified the three main bodies to center the small wire hole on the actual wire spool.  Previously it was offset slightly, as it was centered on the entire body.