Casey’s cartwheel, n. — Green’s Dictionary of Slang

Casey’s cartwheel n.

[proper name Richard Casey, Australian Treasurer who introduced the coin in 1936 to commemorate the Coronation of George VI; the ‘cartwheel’ referred to its unwieldy size of 38.5mm diameter and weight of c.28 gms]

(Aus.) a 5/- piece, a ‘crown’.

1943		Herald (Melbourne) 6 May 5/6: The Australian coins he has designed include all in the range from the halfpenny to the 5/- piece (‘Casey’s cartwheel’) except the 6d.
1949		Dly Teleg. (Sydney) 18 Apr. 3/1: The Australian crown was first minted in 1936, when it became known as ‘Casey’s cartwheel,’ because Mr. R. G. Casey wasthen Federal Treasurer.