Rupert's property is the property of a convex body that permits a congruent copy to pass with positive clearance, without turning, through a straight tunnel cut in the original body (Jerrard et al. 2017, Steininger and Yurkevich 2023). Equivalently, two differently oriented copies admit a common passage direction for which one orthogonal projection lies strictly in the interior of the other, after a possible planar translation.
The cube has this property, and Prince Rupert's cube is even larger than the original cube. A bounded convex polyhedron with the property is a Rupert polyhedron, while one without it is a nopert polyhedron. The Nieuwland number measures the limiting scale factor of a copy that can pass through (Steininger and Yurkevich 2023).
