Antonio Vernucci wrote:

In Europe the hex wrench and spanner size varies in increments of 0.5 mm (a
little more than 1/64"). We then have wrenches of 0.5, 1.0, 1.5, 2.0, .... Very
easy.

Yes, it's a nice system. Incidentally, a "spanner" in the US doesn't seem
to mean the same thing that it does in the UK... here it is a specific kind
of wrench used for retaining rings. I don't know how the usage got to be
different.

In the US, instead of always expressing size as multiples of 1/64" (that is
1/64", 2/64", 3/64", 4/64", 5/64" ...), when possible you simplify the fraction
(that is 2/64" -- 1/32", or 16/64" -- 1/4"). I wonder whether the average
AmerIcan, not necessarily well accustomed to play with fractions, can instantly
determine that, if e.g. a 17/32" spanner is too big, he should try a 33/64"
spanner before taking a 1/2" spanner.

The average American probably can't, but technicians working with the US
system pretty quickly get used to fractional numbers. We probably get a
lot more practice dealing with fractions than you guys do.

Where it gets weird is when you get to very small and very large sizes, the
systems sometimes change. For example, the hex wrenches go down to 1/8",
3/32", 5/64", and 1/16" but then the next one down is 0.050", then 0.035",
and then 0.028". Damned if I know why.

And don't even get me STARTED on numbered and lettered drill bits.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."