Which tool is used to measure the number of threads per inch on a bolt or pipe?

The tool specifically designed to measure the number of threads per inch on a bolt or pipe is the thread gauge. This tool, also known as a thread pitch gauge, contains various blades or templates that fit the specific threads of the bolt or pipe being measured. By aligning the thread profile with the gauge, you can accurately determine the thread pitch, which is essential for ensuring compatibility with nuts, fittings, and other components in mechanical assemblies.

Other tools like calipers and micrometers are primarily used for measuring dimensions such as diameter or length, rather than the specific characteristics of threads. While a measuring tape can be useful for longer measurements, it does not have the precision required for discerning the finer details of thread counts. Thus, the thread gauge is the most suitable and accurate tool for this specific measurement task.