Like many other of our common sayings, the expression “to get down to brass tacks” appears to have alluded originally to some specific operation, something that would call for the removal of successive layers until the brass tacks which held the structure together were exposed to view.
For, as we in America use the expression, it means to get down to the fundamentals, to get to the bottom of a thing, to get to the business at hand.
But the original allusion is lost; literary uses have reference only to the figurative sense, and are too recent to afford any clue to the purpose of the first brass tacks. Because tacks, other than ornamental, are made of copper rather than brass, we surmise that “brass” was a figurative use.
We think, therefore, that the phrase was originally nautical, that the reference was to the cleaning of the hull of a ship, to scraping the barnacles off so thoroughly as to expose the bolts which held its bottom together.
Those bolts were, of course, of copper, but “brass tacks” would be a typical American substitution for “copper bolts.”
The recently advanced supposition that the saying originated from the brass upholstery tacks placed upon counters in drapers’ shops for use in measuring lengths of cloth, seems fanciful to me, for that practice is not old and tacks of that description arc of comparatively modern manufacture.