I've created this individual spool holder with connectors because I wanted to display my filament spools in any way I wanted.

So I took inspiration on the connectors from Joseph Willis connectors video and some simple spool holder I saw somewhere in the internet (sorry I don't remember who so I'm sorry if I'm not mentioning you)

With the connectors choice, all the holders will be fixed to each other and you can use one or both connector between each holder. I used one so far and it is enough.