Various thread diameters and pitch combinations are called a. thread series
What are the basic science terms?
A parallel thread's pitch diameter (also known as its effective diameter) is the diameter of the imaginary co-axial cylinder that intersects the surface of the thread in such a way that the intercept on a generator of the cylinder between the points where it meets the opposite flanks of a thread groove is equal to half the nominal pitch of the thread.
A thread's major diameter is the diameter of an imaginary co-axial cylinder that hits the crest of an exterior thread or the root of an interior thread.
The minor diameter is the diameter of an imagined cylinder that only brushes up against the roots of an external thread and/or the crests of an interior thread.