It would be interesting to work out the mathematical relationship between the crusher section shapes and the object needed, as here, to allow the object to "float" on top of the sections.
Somewhat OT but egg shapes can evolve based on their environment. The guillemot lays conical eggs that won't roll off the narrow ledges on which their parents place them...
https://www.arkive.org/guillemot/uri...ge-A11859.html
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