After World War I, New Guinea was administered by Australia (with an interruption due to Japanese occupation during World War II) until the independence of Papua New Guinea in 1975.
Between 1929 and 1945, special coins were minted for the territory by the Melbourne Mint but Australian coinage circulated too. The coins had the same denominations as their British and Australian counterparts from half penny through to shilling (no larger denominations were issued) but feature a central hole.
The half penny is a one year type. These coins were considered an unsuccessful experiment and were never released into circulation. The Melbourne Mint sold 400 in a set together with a 1929 penny. The rest of the mintage was melted.