MAJOR DIAMETER: The largest diameter of
a screw thread; measured from the crests on external threads
and the roots on internal threads.
PITCH DIAMETER: The imaginary diameter equal
distance between the major and minor diameters.
MINOR DIAMETER: The smaller diameter of
a screw thread; measured from the roots on external threads
and the crests on internal threads.
THREAD PITCH: The distance between a given
point on a thread and a corresponding point on the next
thread. Also referred to as the "lead" which is
the distance a screw will advance during one turn.