Prince Rupert's cube is the largest cube that can be made to pass through a given cube. In other words, the cube
having a side length equal to the side length of the largest hole
of a squarecross section
that can be cut through a unit cube without splitting it
into two pieces.
Prince Rupert's cube cuts a hole of the shape indicated in the above illustration (Wells 1991). Curiously, it is slightly larger than the
original cube, with side length (OEIS A093577).
Any cube this size or smaller can be made to pass through
the original cube.