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.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
Multiple Spindle Drills: http://www.Multi-Drill.com

V8013-R