The British 20-pence and 50-pence coins are both heptagons, which are seven-sided geometric shapes. The coins feature a unique design with seven sides, making them easily distinguishable from other coins. The heptagon shape is also used to represent the seven countries that make up the United Kingdom. The coins are made of copper-plated steel and feature a portrait of Queen Elizabeth II on one side and a design of the Royal Shield on the other.