And I can only assume Phil (Hawkeye) was absent from class when they discussed the DIAMETER of a CUBE??? Either that, or he is still insisting that you can put a round peg in a square hole!
An inscribed circle can be a "diameter". Assuming that: all sides are tangent to the circle and any two opposite sides are parallel, with two adjacent side being perpendicular. A 3' diameter cube would measure 3'x3'. I loved geometry in school! That is the Engineer in me talking.