Thread Terminology 
Major Diameter - It is the largest diameter of the thread which would touch the crests.
Minor Diameter - It is the smallest diameter of the thread which would touch the roots.
Pitch Diameter - It is a middle diameter between the major and minor diameter of screw threads.
Root - Root of the deepest part of the grove that corresponds with the minor diameter.
Flank Angle -This is the angle made by the intersection of the two thread flanks.
Pitch - Pitch of a thread is the distance between 2 crests.
Angle - The thread angle of a screw is the angle between the threads.
Crest - Crest of the thread is the top part of the grove that corresponds with the majr diameter.
Flank - The flank is the angle at which the helix is raised to form a crest.
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