An imaginary cylinder of such diameter and location of its axis that its surface would pass through a straight thread in such a manner as to make the widths of the thread ridge and the thread groove equal; therefore; it is located equidistant between the sharp major and minor cylinders of a given thread form. On a theoretically perfect thread, these widths are equal to half of the pitch.
See also axis of thread and pitch diameter.
Original Posting: 3/20/2012
Last Revision: 2/13/2013
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