Australia 1981 10 cent Sri Lanka 50 cent Mule
In 1981 the Royal Mint in Llantrisant struck many Australian coins. Among them was the Australian 10c piece. At least one example of a 1981 Australian 10c piece is known to have been struck with a Sri Lankan 50c collar die. While the Royal Australian Mint also struck Australian 10c pieces in 1981 it did not strike Sri Lankan 50c pieces, so the mules would have to have been struck in Llantrisant.
No doubt the Royal Mint was striking coins for a number of countries in 1981 when a security edge collar die was accidentally used instead of a reeded edge collar die when striking 1981 Australian 10c pieces. Curiously, no Sri Lankan 50c pieces were struck in 1981: they were struck in 1978 and 1982. Nevertheless, the Royal Mint would have had the dies on hand.
No sales of the mule are known.