Spool stand/shelf for 20cm spools

I had my filament spools stored in a drawer, laying on their side and on top of each other. I always had to take out 2 or 3 spools to get the one I needed.So I designed a simple, modular and interlocking lightweight stand to store the spools in upright position.
They are ~7cm wide and fit one spool with a few mm of wiggle room.

I printed them in rough draft mode at 0.24mm layer height to save time, for better finish I recommend 0.16 or 0.2mm

These can of course be used on every flat surface, e.g. an existing shelf.