Identifying Pitch Diameter

The pitch diameter is the diameter at which the thread tooth and the thread space are equal.

To accurately measure the pitch diameter requires an optical comparator or thread wires.

  • The optical comparator is the easiest to use as the measurement can be directly made and no mathematics is necessary.
    • The disadvantage to the optical method is that the screw must be physically removed from the machine and taken to the comparator. Also, many small shops may not be equipped with a comparator.
    • Measurement over thread wires is an attractive alternative to the comparator for measuring pitch diameter. These measurements can be made directly on the screw. Thread wire measurements are quite accurate, however, they require the use of mathematical formulas along with thread form and pitch information to translate the measurement results into the pitch diameter.

The mathematical formula can be found in the Screw Thread Standards for Federal Services Handbook H28 or other engineering handbooks dealing with threads. Roton’s application engineers can help you with a library of computer software which does all the complex calculations in seconds.

Contact our application engineers for more details and on-line assistance with wire measurements and calculations.

Thread Pitch Diameter