Re: [CAD_CAM_EDM_DRO] Slightly off-topic : History behind lettered drills

In a message dated 10/2/00 12:31:47 PM Pacific Daylight Time,
kjenkins@... writes:

<< numbered drills, I believe are
related to standard wire guages ... but what about
lettered A-Z drills. Where did they come from? Just >>
As long as you are wondering, how come as machine screw sizes go larger the
numbers get larger also, IE a no 12 is larger than a no 4. But the drills to
make a hole for those machine screws get smaller as the numbers get larger.
Also there are several "standard" wire gauges used for different kinds of
wire. And one thing to remember also if you send a plumber to buy 1/2 inch
copper tube it will not fit the 1/2 inch elbows and tees that were bought by
an auto mechanic.
John Meacham
(strong believer in the ISO system of units)