Green’s Dictionary of Slang

1. (Aus. drugs/prison) the equipment (a needle, a spoon, a dropper) required for injecting narcotics [= fit n.² ].

1990		Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Brace and bit. 1. Drug paraphenalia.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 28/2: brace and bit n. hypodermic syringe and needle.

2. excrement [= shit n. (1a)].

2003

B. Dark Dirty Cockney Rhy. Sl. 28: brace and bit shit [...] I’m dying for a brace.