Most threaded products such as fasteners are verified using fixed limit gages when their ability to assemble with mating parts is of primary concern. However, disputes may arise that require direct measurement of the threads. Other applications may require such measurements as part of basic quality requirements, for statistical process control, or machine setup. When “go/no-go” answers are not enough, the pitch diameter of the thread is usually the first—and most critical—element of the thread that is measured.
Two problems can be encountered when disputes are the reason for the measurements. The first is that fixed limit gages engage (or not) most elements that make up the thread while pitch diameter is only one of those elements. The second problem is that there are several instruments used to measure pitch diameter but they are different in how they do the job.