According to :

And finally nails, screws, wire, etc.....
I am going to turn this into a question....
Is a #16 common nail 16 cm long? Is a #8 screw a metric number? (of
course the length is still in inches).
Is a #12 guage wire in metric, or what does that "12" mean?
I'm just guessing on this, I dont know metric well enough...

The above are purely arbitrary naming conventions, they don't
have any direct relationship to specific measurement systems.

And how long is a 16d nail anyway? First, you need to know what
_kind_ of nail it is. Back when they were really measured that
way, you also had to know the inflation rate.

And just how big is a barrel? It depends on what you put in
it. There are dozens of different size "standard" barrels
in the US alone.

SAE/Imperial grew by accretion by a whole host of arbitrary
"measures" which weren't measures of the relevant things.
I mean, indicating nail length by how much a 100 of the things
cost more than a century ago? Is that silly or what?

The value of metric is that all of the measures (length, weight,
volume etc) are directly related by simple rules. And secondly,
things specified by metric are actually based on _measurements_
other than bizarre centuries old irrelevancies.

Wouldn't it be nice to know how big a #36 or "A" drillbit is
without having to resort to a book?
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.