I googled for the proper spelling of "Reuleaux triangle", and Wikipedia's article has this: > Because all diameters are the same length, the Reuleaux triangl

I googled for the proper spelling of "Reuleaux triangle", and Wikipedia's article has this: > Because all diameters are the same length, the Reuleaux triangle, > with all other curves of constant width, is an answer to the question > "Other than a circle, what shape can you make a manhole cover so that > it cannot fall down through the hole?" http://en.wikipedia.org/wiki/Reuleaux_triangle http://en.wikipedia.org/wiki/Reuleaux_triangle