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1. Plastic
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is there a formula to figure out dpeth of treads by turning thread gauge down to bottom and counting on way out. ( i think you use the second number ex:1\4-20. twenty turns equal 1 inch thank you.

2. Cast Iron
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## You've got it.

That's one way of doing it; I'd use a depth micrometer if you're looking for any type of accuracy.

If you're just getting a rough estimate, your method works. Simply divide 1" by the number of threads per inch, in the 1/4"-20 case, 20. This will give you 0.050", which is the lead of your thread. Lead is the amount the thread advances linearly with a single rotation.

So, the number of rotations multiplied by the lead gives you the depth. Of course, this isn't accounting for the fact you have no way of measuring the rotations of the gage with any degree of precision, nor is it taking the thread fit into consideration.

3. Don't forget to add the chamfer depth at the top of the hole (where the thread gage releases) to your depth calculation. -Mike

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