I can’t really think of a better example, but well, if you stack half-cylinders like these:
…they can’t be off-center in the direction that they’re rounded, because gravity + their shape pulls them towards the center.
And well, this saddle shape is rounded in two directions, so it pulls towards the center in both directions.
It’s also better than a parabolic/lens shape, because while that can’t either move sideways, it doesn’t counteract angular movement, so the stack would still bend and fall.
I can’t really think of a better example, but well, if you stack half-cylinders like these:
…they can’t be off-center in the direction that they’re rounded, because gravity + their shape pulls them towards the center.
And well, this saddle shape is rounded in two directions, so it pulls towards the center in both directions.
It’s also better than a parabolic/lens shape, because while that can’t either move sideways, it doesn’t counteract angular movement, so the stack would still bend and fall.