[SteveC]

Richard

You may find the following of interest.

[url]http://www.osv.org/explore_learn/document_viewer.php?Action=View&DocID=1973[/b][/url]

[url]http://en.wikipedia.org/wiki/Screw#Unified_Thread_Standard[/b][/url]


Here's a couple of tips I found at the below listed link.

Newman Tool's handy hint.

For Metric sizes only. Diameter of thread minus the pitch equals the tap drill size.
eg. M6 x 1
6 - 1 = 5mm
and you thought metric was difficult ;-)




thanks to Jay Steinbuchel of Barksdale Control Products for the following:


This works for all 75% threads, not just metric.


For example, the tap drill for 3/8-16 is 5/16.


The pitch is 1/16". (1 / threads per inch = inches per thread)


3/8 - 1/16 = 5/16.


For other sizes that don't work out so nicely, just use the closest drill size.

http://www.newmantools.com/tapdrill.htmhttp://www.newmantools.com/tapdrill.htmhttp://www.newmantools.com/tapdrill.htm

 

[SteveC]

Well Charles,

Invest $40 and buy a cheap 115 piece drill set from Harbor Freight. While the drills aren't anything to write home about, the hinged cover index itself is worth the money and you could always upgrade the drills as they wear out or break.

115 Piece High Speed Drill Bit Set with Index
29 fractional sizes 1/16'' to 1/2''
26 letter sizes A to Z
60 numbered wire gauge sizes 1 to 60