What's the origin of the expression " to get down to brass tacks"?What's so fundamental about brass tacks?

'The brass tacks that you get down to (1897) are probably the ones used to measure cloth on the counter of a dry goods store, suggesting precision.' www.etymonline.com

That doesn't sound very convincing to me, though. Does the phrase 'brass tacks' suggest precison, or is it used more often to suggest something like 'the bottom line' or 'the nitty gritty' - the hard facts of a situation?

To me (just a guess) the phrase suggests the wearing away of upholstery, or maybe soft shoe leather, to show the solid, 'true', structure underneath.