Green’s Dictionary of Slang

(S.Afr.) a 375ml half-bottle of spirits or wine.

1953		Lanham & Mopeli-Paulus Blanket Boy’s Moon 70: He took from his pocket a half-jack of white man’s brandy [DSAE].
1966		J. Bennett Hawk Alone 122: The baas, he brought a half-jack with him. I see it in the car.
1970		H. Kuper Witch in my Heart III i: The White people call it brandy. It looks like golden water, and after half a jack you are sweet all over.
1975		S. Roberts ‘All That Jazz’ Outside Life’s Feast 48: He’d been tippling from a half-jack he had in his pocket.
1975		Casey ‘Kid’ Motsisi ‘Kid Haja’ in Casey and Co. (1978) 59: She comes back carrying a ha-ja of mahog and a glass.
1980		B. Setuke ‘Dumani’ in Mutloatse Forced Landing 58: The amateur gangsters who pay their way to and from the ghetto by bribing the barrier-attendants with a nip of ‘ha-ja’ of mahog as they pick the pockets of innocent passengers.
1982		P. Slabolepszy Sat. Night at the Palace (1985) 42: He takes a swig from his half-jack and offers it to Forsie.
1987		(con. 1950s) G. Moloi My Life 115: They were on their way to Nomali Mshengu’s shebeen [...] The order there would be six quarts of beer, half a jack of Mellow Wood.
1995		S. Jacobs Enemy Within 113: Three of us shared some beers and a half-jack of brandy.
2005		A. Lovejoy Acid Alex 100: The teacher [...] was called Bols – from Bols brandy, because he always had a half-jack in his desk drawer.
2011		Mail and Guardian (Johannesburg) 13 May 🌐 He would zip off to the grimy press bar [...] and return with a half-jack of something truly vile.