Green’s Dictionary of Slang

(Aus.) a stockman; thus stockbanging n., working on a cattle farm.

1934

A. Russell Tramp-Royal 209: A desire took possession of me to take a turn at stockbanging. [Ibid.] 212: Young gins are also employed in this capacity and often make better stockbangers than the ‘boys’.

(US prison) a convict who curries favour with the authorities.

1933		Ersine Und. and Prison Sl.
1950		Goldin et al. DAUL 212/2: Stockholder. (P) A convict who works so zealously in the state’s interest that he is held in contempt by fellow prisoners.

the genitals.

[1861		(con. 1840s–50s) H. Mayhew London Labour, London Poor IV 248/1: They call me ‘Old Stock;’ why I shan’t tell you, though I might easy, and make you laugh too, [...] I was once the swellest woman about town].
1890–1904		Farmer & Henley Sl. and Its Analogues.