Unusual Coins

Some other coins, like the British Fifty pence coin and the Canadian Loonie, have an odd number of sides, with the edges rounded off. This way the coin has a constant diameter, recognisable by vending machines whichever direction it is inserted.
The triangular coin (produced to commemorate the 2007/2008 Tutankhamun exhibition at The O2 Arena) was commissioned by the Isle of Man, became legal tender on 6 December 2007. crown). Other triangular coins issued earlier include: Cabinda coin, Bermuda coin, 2 Dollar Cook Islands 1992 triangular coin, Uganda Millennium Coin and Polish Sterling-Silver 10-Zloty Coin.
Guitar-shaped coins were once issued in Somalia. Poland once issued a fan-shaped 10 złoty coin and the 2002 $10 coin from Nauru, was Europe-shaped.
Some mediaeval coins, called bracteates, were so thin they were struck on only one side.