Green’s Dictionary of Slang

(Aus./S.Afr.) a threepenny piece.

1887		Illus. London News 26 Feb. 2/1: South African [...] slang colloquialisms [...] A penny piece, which is abhorred by the natives, is a ‘debblish’ [...] a threepenny piece is invariably a ‘pen’.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1941		Baker Popular Dict. Aus. Sl.