The phrase get down to brass tacks (not brass tax) is an Americanism dating from the 19th century. In the idiom, brass tacks means (1) the essentials, or (2) the basic facts.
The phrase’s exact derivation is unknown, though there are a few theories. One is that the expression is inspired by the centrality of brass tacks in furniture and upholstery. Another is that brass tacks is simply a bit of rhyming wordplay derived from facts. In any case, the phrase was widespread in its modern sense by the early 20th century.
Examples
Most early instances of brass tacks are from U.S. publications—for example:
After two months of preliminary activity, speculating and theorizing, the legislature gets down to brass tacks this week. [Chicago Tribune (1909)]
Germany early got right down to brass tacks. [New York Times (1918)]
There wasn’t a sign of a wrangle and when they got down to brass tacks more than half an hour was consumed in bringing about an oral agreement. [Providence News (1919)]
Today, however, brass tacks is used throughout the English-speaking world—for example:
But what you cannot see, what in fact you rarely find in Florentine Renaissance art, is a brass-tacks portrayal of merchant life. [Guardian]
But only one speaker really got down to brass tacks. [Toronto Star]
As the talks get down to brass tacks this week the parties are entrenched firmly in three camps. [Stuff.co.nz]
