Use 48mm (OD) net cups on your 3D printed hydroponic tower.
It fits with the following model:
https://www.thingiverse.com/thing:3405964
https://www.printables.com/de/model/62110-hydroponic-planting-system-modular
Warning: The ring is not fixed to the tower. I only use net cups on the tower as long as the plants are small. When they grow bigger, you should use the bigger and printable cups that come with the model of the hydroponic tower!
The author marked this model as their own original creation.