Reciprocal Reuleaux Triangle for FDM (Q55404)

This is a square solid inside a triangular hole within a triangular solid inside a square hole. The predecessor to this design featured a triangle inside a square hole within another triangle inside a square hole. It sounded nice but the square hole broke up the symmetry of the triangle, plus it didn't exploit the reciprocal capability of a reuleaux triangle to contain a square inside a triangular hole.