Green’s Dictionary of Slang

(Aus.) a threepenny bit.

1913		Sport (Adelaide) 4 Oct. 4/2: Pomp H, the spendthrift, murdered a trut on chewing gum .
1937		Mirror (Perth) 18 Dec. 25/5: Thrifty parents can stop saving their ‘thrummers,’ ‘truts,’ ‘tray-bits,’ or whatever happens to be the current vernacular for three penny bits.
1943		Baker Popular Dict. Aus. Sl. (2nd edn).