Thread: A continuous projection with a specified tooth shape formed along a helix on a cylindrical or conical surface.

External thread: A thread formed on the outer surface of a cylinder or cone.

Internal thread: The internal thread formed on the inner surface of a cylinder or cone.

Large diameter: The diameter of an imaginary cylinder or cone that is tangent to the apex of the external thread or the base of the internal thread.

Path: The diameter of an imaginary cylinder or cone that is tangent to the base of an external thread or the apex of an internal thread.

Middle meridian: The diameter of an imaginary cylinder or cone whose bus passes through the grooves and bumps of equal width on the tooth type. The imaginary cylinder or cone is called a middle diameter cylinder or middle diameter cone.

Right hand thread: The thread that is turned in during clockwise rotation.

Left-hand thread: The thread that is spun in when rotated counterclockwise.

Profile Angle: The Angle between the sides of two adjacent teeth on the profile of the thread.

Pitch: The axial distance between two adjacent teeth corresponding to two points on the median diameter line.