The formula is so simple that the only thing I use charts for is to
convert drill sizes to decimal inch. Tap drill size is the outside
diameter of the***minus the pitch (or 1/number thds/inch). Example:
3/8-16 tap drill is 3/8 - 1/16 = 5/16", 1/4-20 tap drill is
1/4(.25)-1/20(.05)=.200". This formula works for standard and metric
threads, the nice thing about metric is they give you the OD and the
pitch! I saw this in a book in the library and haven't met many
machinists that knew of it. It's good to know in case you have to tap
something that isn't on the chart, perhaps 1/4-32 glow plug threads.
> I forgot the rest of the words...
> Many thanks to engine guru George Aldrich for posting upon his website the
> BEST cotton-pickin' drill & tap size chart this Cajun ever did saw... Once
> you figger out the color key, this rascal has it ALL, up to 1"..... Big
> enuf for me...
> http://www.FoundCollection.com/;Just click the link..