Green’s Dictionary of Slang

(Aus. und.) a watch.

1895		Crowe Aus. Sl. Dict. 83: Tail Block, a watch.
1901		Argus (Melbourne) 20 Sept. 6/4: The watch is otherwise known as a yack, a tail block, or with chain attached as a block and tackle, while the man who has a weakness for watches [...] is called a thimble twister.