Hi Dave and thanks for the chart.

If you check the drill sizes across the chart, you will find that it is even easier.

For the 75% thread depth, just deduct the pitch from the overall diameter !!!

Eg 1”x 8, tap is 7/8”

?????? M6 x,1 tap is 5

???? ??3/8” x 16, tap is 5/16”???? etc.

Works every time.

????????? Ellis

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Here chart I have used since 1970's?
Still hangs on the wall this a photo great help.?
I also have a drill chart upto 1 " with number,? letter , metric and fraction for 1970's. It great help but you can buy online and hang on wall.?
Dave?