11/16 UNEF Drill size

As a young lad I am blessed with the use of 60 degree threads that are now widespread. It’s easy to work out the drill size as all you have to do it minus the pitch from the OD and you get your drill size.
I have a project at home and I need a big fine thread. I looked through my late grandfather’s tap box and found a 11/16 -24TPI tap. I’m just wondering on the tapping drill size as this seems to be a non standard thread.

Kind regards,

J.

According to my Tracy Tools wall chart that is a UNEF thread , and their recommended tapping drill is 16.25 mm dia .

If you are blessed with the formula, why not just use it!

Diameter is 11/16” = 0.69” (0.6875)

Pitch is 1/24” = 0 0417 (0.04166)

Diameter - Pitch = 0.6875 - 0.04166 = 0 646”

If you type your topic title into Google, exactly as you have written it, you will find the answer to your query.

E.g. https://www.gewinde-normen.de/en/unified-extra-fine-thread.html

It will also suggest you use a drill sized at 16.6 of those new-fangled continental millimetric units rather than the bizarre not-in-any-standard-range imperial number quoted above.

For those unable to work out the metric size, 0.646 * 25.4 would provide the metric drill size.

I expect the imperial drill size could easily be provided as a fraction, if really required. Just a bit more simple maths.

83/128ths I think

Roy

That’s great thank you!

David