3/8 NPT Internal Thread Tolerance

[ddeno]

Does anyone know the formula to calculate the acceptable min/max diameter for an internal 3/8" NPT?
Thank You!

 

[racookpe1978]

The thread is usually already provided by the part or assembly (as a screw in fitting or valve for example) or is very simply - almost automatically - done by a commercial tap purchased already cut.

Don't get me wrong, there are tolerances in the threads, taps, dies, and parts involved, but unless you are somehow needing to write a CAD/CAM program to actually drive the machine - just specify the thing.

Put the pipe dope or Teflon (properly wrapped) on the threads and go.

 

[ddeno]

Thanks racookpe1978 but I am in need of the formula.

 

[Compositepro]

With a taper thread you can easily tap too deep or not deep enough and get the diameters wrong. I would look in the Mahinery Handbook if I could find mine right now. I'm sure you could find the specs with Google as well.

 

[ddeno]

Thank You Compositepro but I could not find the formula information in the Machinery Handbook or on Google. I am beginning to think this formula is a well kept secret!!

 

[Canadieng]

I don't know of the formula, but how about a chart from Machinery's Handbook as attached?