Strangely Shaped Coins and Wheels that aren't Round

When I lived in the UK I used to sometimes wonder about the strange shape of the 50 pence coin.  It seemed to be half way between round and hexagonal (actually it has 7 sides).  According to this blog post the shape of the coin means that it has constant width even though it isn't round.  The post shows how this works and even demos using them as wheels.