[ATM] Need help with metric thread

[Glen Youman <gyouman@sbcglobal.net>]

I'm planning a non-standard adapter for my scope.  It will consist of two pieces that screw together using metric thread.
   
  The male part will have a nominal diameter of 1.96 inches and will be threaded with 0.75 mm thread (thread depth 0.0185 inches).  My question is what should the nominal interior diameter of the female part be to assure a 70 percent thread engagement?
   
  There must be a simple formula but a search of the internet reveals all kinds of data about thread profiles, taps, etc. but no formula.
   
  Any help would be appreciated.
   


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Glen Youman
Penryn, California
http://www.astrophotos.net/ - Home page
http://astro.sci.uop.edu/~sas/ -Stockton Astronomical Society
http://www.darksky.org - International Darksky Association
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