There was no need for the Mint to produce any pennies in 1933 because there was no commercial demand, and it held plenty of stock. There was a custom at that time for the King to place a set of coins of the current year under the foundation stone of important new buildings, and the Mint struck three 1933 pennies for this purpose, also one each for its own museum and for the British Museum, and at least two others. The result was a rarity that people thought might turn up in their pocket change, and that is probably the best-known British rare coin.