There's a thread in the BS ("Below the line") debating people's experiences with conversion (or non-conversion) to SI measures from the Imperial system, as it was once known. Without wishing to bring the merits or nonmerits of such conversions 'above the line' it occurred to me that there were many expressions we all use that derive their power from the older systems and that appear to have no replacements using SI units. There may be others that have appeared in SI units that had no direct equivalents in Imperial measures, although none yet come to mind.

To start off, a couple that have no SI equivalent include

"A country mile" which, in Oz, still means 'a distance known to the speaker that has relevance to the listener but for which there is no "real" value"

and

"Give him an inch and he'll take a mile", most often used (in my experience) by young women when dealing with young men with exploratory and amatory intent.

I'm sure there are many others I once knew and still more that I've never heard. but that 'catters have in their repertoire.

Cheers, Rowan