I wanted a way to keep all my toppers organized while also being easy to access, I use a lot of gridfinity parts so I felt like it was an excellent fit. :)

Each bin needs a screw/bolt with a standard m6 machine threads, thread directly into the plastic. 12mm length minimum, the hole length is around 7mm, and your topper won't have much to grip if it was any shorter. Print at 0.2mm layer height.
 

Notes:
I recommend threaded rods/grub screws that you thread from the top (stop when you hit the larger hole), otherwise thread from the bottom. The hole on the bottom is sized to accommodate an m6 socket screw head. I recommend a longer screw for sunken heads or heads with m6 adapters screws inside (like some bat tops), however if your topper is hollow you could scratch the insides by using too long of a screw wound too tightly. Maximum topper diameter* is 42mm. I have not tested it with magnets, but if you find this a problem consider using stainless steel hex heads/screws instead.

*if you want it to play nice with other gridfinity parts, anyways.