Melbourne began experimenting with a new coinage for the penny and halfpenny in 1919. The new coins would be of nickel and would be square with rounded corners so the there would be no confusion with the silver coinage.
The coins were designed and experimental dies were prepared locally. Trials were made and distributed. The Mint Deputy Masters clearly believed that this new coinage had Commonwealth support; even the Sydney Mint in its annual report of 1919 mentioned the new equipment it would need for bronze and nickel coin production.
In 1920 the Royal Mint, London was asked to prepare working dies for the nickel coins and supplies of nickel were purchased in readiness for full scale production. However the Commonwealth never legislated for the new nickel coins and Australia retained the large bronze formats until the introduction of decimal coinage in 1966.