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11/16 UNEF Drill size

I need to know the drill size or how to calculate it myself.

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Jayme Gisbourne02/04/2021 16:44:13
11 forum posts

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.

Trevor Drabble02/04/2021 16:50:49
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339 forum posts
7 photos

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

not done it yet02/04/2021 17:40:14
7517 forum posts
20 photos

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”

DC31k02/04/2021 17:49:39
1186 forum posts
11 photos

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.

not done it yet02/04/2021 17:59:05
7517 forum posts
20 photos

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.

roy entwistle02/04/2021 19:22:31
1716 forum posts

83/128ths I think

Roy indecision

Jayme Gisbourne02/04/2021 19:41:07
11 forum posts
Posted by Trevor Drabble on 02/04/2021 16:50:49:

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

That’s great thank you!

David Noble02/04/2021 20:30:24
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402 forum posts
37 photos
Posted by roy entwistle on 02/04/2021 19:22:31:

83/128ths I think

Roy indecision

angel

David

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