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Drill bits, I'm talkin' about...
http://dimar-canada.com/drill_size/drill_size.html

What is the origin and purpose of the lettered bits?
The numbered series running backwards similar to gauge, makes sense, but lettered mixed in?
To make matters even more confusing there seems to be some overlap and repetition(?).
If I wanted some smaller bits than 1/8" is there a better chucking system than the standard 3/8" or 1/2" drill chuck?
 

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Drill bits, I'm talkin' about...
http://dimar-canada.com/drill_size/drill_size.html

What is the origin and purpose of the lettered bits?
The numbered series running backwards similar to gauge, makes sense, but lettered mixed in?
To make matters even more confusing there seems to be some overlap and repetition(?).
If I wanted some smaller bits than 1/8" is there a better chucking system than the standard 3/8" or 1/2" drill chuck?
letter bits are the fit in between the 1/64" increment bits...
read the decimal places for letter bits... they incrementally increase.. hence the over lap..

swap out your chuck for a 0 (zero) to 3/8 or 1/2"...
get a pin vise for the really small bits... capacities range from .000-5/32"...
number bits run from 1 through 100 but it will tough to find anything readily available under a #80...
number drills are a perfect fit for orifices and jets..

 

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Some of the lettered bits are the perfect size for taps, if you are really concerned about the per cent of threads you wind up with. I was looking for replacement chucks on eBay a couple of years ago and some of the smaller chucks were down to very small sizes. The 1/2" ones usually only went down to a 1/16 minimum. There were chucks that were worth $1000 there but I doubt any of us need that kind of accuracy. As far as I know NASA isn't making parts out of wood.
 

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It's all about clearance. Depending on the application of the job or the hardness of materials being tapped you may be using a different percentage of thread engagement. The Pocket Ref, Marks Machinery Handbook, and the other reference books have chapters on what tap drills are to be used for every situation, you wouldn't think there was that much of a science to it.

Tap Drill Size Calculator -- Technical Notes

I have a nice little pin vise that I never use, instead I have a 1/4" hex shank drill chuck that I picked up from either Grizzly or Harbor Freight that works well. It looks similar to this one on Amazon.

http://www.amazon.com/Neiko-4-Inch-Keyless-Chuck-Conversion/dp/B007TCHKXW/ref=pd_cp_hi_0

I have an old 1/4 inch chuck black and decker drill from eons past that does a fantastic job of holding small bits.
 
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