The UK is unique.
We are Metric,
except we still use
some imperial units.
We use mm, meters, grams, Kilograms, litres, millilitres. But we use miles on our roads. People will still use feet and inches.
How to upset both a European and an American, quote both in the same sentence (which I sometimes do
). Its "6inches long, + or - a few millimetres".
Carpentry is still done in imperial units, however, everything is sold in metric units, so 6inch nails are 100mm, 3x2 is 75x50 mm (but with a slight oversize), etc.
Distance is in Miles on the roads, but fuel is sold in litres.
In my youth, I once asked for some 1" stainless steel bar a couple of feet long, from the offcuts bin. The retailer told me (pompously) they where a metric establishment, so I asked for 25mm bar, about 300-600mm long. I heard him out the back asking the warehouse man for the 25mm bar ..... I heard the warehouse man yell " any inch S.S. bar a couple of feet long in the offcuts bin" to his companion, still makes me smile.
Just remember the British are contrary.