This high quality, custom set of Thread pitch gauges contains all the thread sizes commonly used in band instrument repair. Use this tool to find the thread pitch on any screw.
To use the thread pitch gauge, simply match the threads on any screw or rod to the ridged edge of the corresponding leaf. American Unified threads (UNC, UNF) and metric threads are defined by two dimensions, the thread size and the thread pitch. Unified threads use nominal gauge sizes for the thread diameter and threads-per-inch (TPI) for the thread pitch. For example: A 3-48 thread means the thread is 3 gauge (0.099 inch major diameter) and has 48 threads per inch. Metric threads use the actual major diameter (outside diameter of male threads) in millimeters for the size, and the distance between threads for the pitch. A M2.5x0.45 thread has a major diameter of 2.5mm and a pitch of 0.45mm.
To determine the threads on a rod or screw: First measure the major diameter with a digital caliper and compare it to this table of threads. Male threads are cut with a certain tolerance for how tight they will fit. This means the measured diameter will almost always be slightly smaller than the defined thread size. Every thread size has certain pitches that are commonly used, typically only two or three. Once you have determined the size you will have a narrow list of potential pitches. Use the thread pitch gauge to find which one matches your threads. Special thanks to Jerry Gilbert and Wayne Tanabe for making this chart available.
Screw Pitch Gauge Metric: 0.25-2.5mm threads
Screw Pitch Gauge Standard: 4-84 standard threads