Green’s Dictionary of Slang

(Aus.) (in WA) a very small glass of beer served in a pub.

1966		S.J. Baker Aus. Lang. (2 edn) 229: In Brisbane and Sydney, 7 oz. measures are sevens, but in Perth clubs the nearest measures (6oz.) are bobbies.
2006		P. Brown Three Sheets to the Wind 241: Once you’ve mastered these technicalities, you might want to try ordering a pony, a bobbie, a ten, eight or six, a handle, a seven, a butcher, or simply a glass - or perhaps a small glass.
2011		Gigglewater: Get on the Turps in Aus. 18 May 🌐 Beer also comes in bobbies, ponies, sixes, cans, stubbies, throw downs, and grenades, long necks.’ Pretty confusing eh, mate?
2018		Bottlemart:Drinkspiration 🌐 For those with an extra large thirst, the Jug is for you. Available in most States, the Jug is a 1140ml behemoth of beery deliciousness. It’s not an actual glass on its own [...] it’s a jug which you’ll usually share with your mates by pouring it into a Pony, Bobbie [...] or Pint glass of your choice .