Green’s Dictionary of Slang

1. a needle.

c.1701		N. Ward Three Nights Adventures in Reformer 87: [T]he Spirit of Malt had such an influence on the Steel Bar, that it [...] made it far swifter of motion than a Weaver’s Shuttle.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1822		Egan Life and Adventures of Samuel Hayward 8: The thoughts of throwing about the steel bar* for the remainder of his days were insupportable to him. [*A needle].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.

2. a measure of gin, when added to another form of alcohol.

1823

Rambler’s Mag. 1 Mar. 132: Give me a tumbler of flickery and put a steel bar in it (that is a pint of sherry and a quartern of gin, to make it palatable).