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hole wizard NPT taper tap drill size issue

Question asked by Michael Gera on Mar 7, 2016
Latest reply on Mar 7, 2016 by Michael Gera

The attached part has an 1/8" NPT taper tapped hole and (4) 1/4-20 tapped holes.

 

If you measure the diameter of the 1/4-20 tapped holes, it shows the correct .201 (#7 drill) size.

 

If you measure the diameter of the 1/8" NPT taper tapped hole in the center, it shows .417", which is much larger than the correct .332" tap drill size.

 

If this part were sent to the laser, there would be no material left for the 1/8" NPT taper tap .

 

Is there a way to fix this?

 

Why is the hole sizing correct for machine tapped holes but not taper tapped holes?

 

Thanks.

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