I have been meaning to reply to the inquiry about letter, number and 
fractional drills, the whys and wherefores thereof.

A newbie beat me to it.

Welcome aboard, Lamar.  You are gonna love it here.

On Wednesday, March 10, 2004, at 06:02  AM, Lamar keeney wrote:

>
>   RE:As for the drill bit lettery and number system.Having been in the 
> machinenist program before returning to carpentry. The use of them was 
> to allow for minor dia. of threads of different classes of fits,also 
> tolerace of holes for bolts.This also applied to pre-drillng of holes 
> for reams and such.