When the thread is designed, the thread flank angles, crest and root radius or other form is established, and tolerances and allowances between mating threads are determined. The pitch diameter is the point on a thread where the distance between two points on the thread flank is 1/2 the pitch. For a given external thread nominal diameter, this pitch line is established and tolerances applied. The internal thread pitch diameter is then calculated for a designed allowance (minimum clearance) and tolerances applied to it.
Check table 4. My 22nd ed of Mach. Handbook shows max and min Pitch Diameter for external (and internal) threads. There is a long hand way to compute via equations any thead size... but hopefully table 4 will do yah.
This may be a little late considering your query was in April. However, I have found that going to the source is useful. The Machinery's Handbook got its information from the thread specification ASME B1.1. Look there, specifically in paragraphs 5.8 and 8.3. Paragraph 10.1, with its associated figure and tables, might also be of interest. Good luck.
