Stackable Raspberry Pi Case with 40mm fan

I have many Raspberry Pi 4 and was trying to create a stackable solution, so to have all the raspberries with 40mm fan one over the other using as less space as possible and have access to all of its features.

The front and back pieces are glued together using any glue for PLA, I have used loctite, after gluing it you just screw your Raspberry Pi to it, print 4 bullets and another set of case pieces (front and back) which you will have to glue as well. To this set you recently created you screw your 40 mm fan cooler, in case you don't want a fan cooler you could reduce the bullet size, and on top of those lastly printed case parts you can screw another Raspberry Pi sbc