Chess box
Two identical halves (2×4 · 4×4 · 2×4 squares, every edge mitred at 45°). One lies face-down as the base;
the other turns 90° and drops over it. Closed: 4×4×2 squares, checkers on every face.
Hinge
Closure
Every flap end has a brass key on its hinge half and an open-ended groove on its far half,
both set toward the inner heel of the mitre where the wood is thickest. As the lid drops, each key’s chamfered nose finds a groove,
so no wall can swing or shift. Magnets in the 4 meeting edges hold the lid down. Only a straight lift opens it.