"Joe AutoDrill" wrote in message
news:QoOOi.1702$d2.971@trnddc08...
I don't know about the letter series. I suspect that, as Ed says, they
were created to fill in awkward gaps in the decimal set.

Almost looks as if letter sizes were made to go beyond a #1 drill... In
other words in order from small to large: 4,3,2,1,A,B,C,D,...
--


Regards,
Joe Agro, Jr.


Some more research indicates that the "Stubs steel wire gage" extended into
letters that exactly match the letter drills. They indeed extend fairly
neatly from the number series. The step to number 1 from A is pretty darn
close to the step from number 2 to number 1.

This supports my contention that in this chicken and egg problem, the wire
probably came first.

I also suspect that, in terms of twist drills, the number and letter sets
may predate the fractional series. For the most of metalworking history, we
made things to fit, not to dimension.

When we started making thing to dimension, fractions based on a power of 2
were a natural choice. If you had an inch standard, and a small enough set
of dividers, you could lay out a 1/64" rule.

Measuring things in thousandths is a fairly recent concept, attributed to
Henry Ford.

You could make drill bits in 1/1000 increments but you would be making then
in smaller steps than they accurately drill holes.

The system we have now functions reasonably well. The only improvement a
decimal series of drills would have, is that they are easier to remember.
Heck, I have enough useless information rattling around in my brain. when I
need to know a drill size, I look it up on the chart.


Paul K. Dickman