PMC Mercury 60 Degree Metric Thread Measuring wires are the best sizes for metric threads. They may be used with other forms or with special pitches, constants for which may be calculated from the formula provided below. Our wires (three per set) are made from selected high-speed steel, are extremely accurate in roundness and straightness and are within 0.000020” (20 millionths) of exact size.
The formula for determining wire constants for all 60° threads = 3W -0.866025P. Where W=actual average wire size and P=Pitch (1/TPI).
The most accurate and universally recognized method of obtaining pitch diameter measurements of thread plug or setting plug gages is by means of using three hardened steel measuring wires laid into opposite sides of the thread. Please reference PMC Mercury Handbook #37 for additional information.