Hi everyone!
This modular paint rack is 20 cm wide and comes in two slot sizes: 28 mm with 6 slots, and 34 mm with 5 slots. 

You can freely mix and match them according to your paint storage needs.
In theory, it can be extended infinitely, but in practice—considering the weight of the paints—please limit a single rack to a maximum of 8 tiers. The attached photo shows an incorrect usage example—please do not imitate it.