You can’t put a hole in the Queen’s head

» Bristol Times uncovered the story of how the 50p coin is a Bristol invention a couple of years ago.

The distinctive seven-sided shape of the coin was the solution to a complex engineering problem. The 50p coin was to replace the old ten shilling note, because coins are more economical.

The new coin, though, had to look and feel different from the others, especially for the benefit of the blind or partially-sighted.

It couldn’t be circular, because banks and businesses counted large quantities of coins by weighing them, and so a 50p piece would have to be five times the weight of a 10p piece, which would have made it the size of a digestive biscuit, and considerably heavier.

The 50p would have to opt out of the weight system, but if it was recognisably larger than the 10p (which was far bigger in the late 60s than modern 10p coins) then it would be impractical. It would have to be a different colour or a different shape.

The Royal Mint couldn’t find a suitable metal that was sufficiently different in colour, so a new shape it would have to be.

You couldn’t have a coin with a hole in the middle as it had to have the Queen’s profile on one side, and you can’t put a hole in Her Majesty’s head.

The only engineer on the Decimal Coinage Board was Hugh Conway, MD of Bristol Siddeley Engines, and he took the problem to the engine design office at Filton. Here, one of the staff, Colin Lewis, came up with the sevensided solution, and the shape was drawn out. Stainless steel samples were made by toolmaker Percy Stone and a perspex channel simulating a vending machine slot was made to show how the coin would roll down it.

Conway took the sample coins and slot to a meeting of the Decimal Coinage Board, where the idea was accepted. It was a simple and yet ingenious triumph of old-school Bristol problemsolving, and the design has since been copied all over the world.

» The full-length version of the original BT article is on the Post website at

Lord Fiske (left) Chairman of the Decimal Currency Board and Sir Hugh Conway (right), MD of Bristol Siddeley, unveiling the 50p coin design in 1968