What feature of a thread does a thread micrometer check?

A thread micrometer is a precision measuring instrument specifically designed to check the pitch diameter of threaded components. The pitch diameter is the theoretical diameter at which the width of the thread groove is equal to the width of the thread flank, making it the most important dimension for ensuring proper fit and function of mating threads. This measurement is critical because it ensures that the external and internal threads engage correctly, allowing for smooth operation and assembly without excess play or tightness.

While the major and minor diameters are also important features of a thread, they are typically measured with different tools, such as calipers or special thread gauges. The thread angle, which refers to the angle between the flanks of the threads, is another critical characteristic but is usually checked with specific measuring fixtures or gages rather than a thread micrometer.

Thus, the primary role of a thread micrometer is to accurately measure the pitch diameter, making it essential for proper thread identification and quality control in machining operations.