[dancek]

I don't know what's natural, but I live in Finland where we use the metric / SI system extensively. Some people don't even know how long an inch is, let alone a foot.

Recently I was building a roof with an old, very experienced builder. Turns out that on construction sites, nails and planks are always discussed in inches, even when they're actually metric. So a 60mm nail would be "a two point fiver" ("kakspuokki" or such in Finnish).

[Hondor]

The reverse is true for metric pipe threads. They're named with mm but are actually the same dimensions as the inch threads. Luckily the inch numbers have only an arbitrary relationship to any dimensions of the thread anyway so nobody will get confused trying to measure them.

[exDM69]

The sizes of lumber and other construction materials are inch based, rounded to mm, even in Finland. Instead of 1/4", 1/2", and 3/4" we have 6.5mm, 12mm and 18mm.

Note the inconsistency in 1/4".