Thread Pitch Chart — Metric & SAE Thread Identification
Thread pitch is the distance between adjacent threads, and getting it right is essential when matching a bolt to a nut or tapped hole. This chart covers metric pitch in millimeters and SAE threads-per-inch (TPI) for every common bolt size, plus how to measure pitch with a gauge or a ruler.
Metric thread pitch (coarse vs fine)
Metric bolts come in coarse and fine pitch. An M10 coarse bolt has a 1.5 mm pitch while M10 fine is 1.25 mm. Coarse is the default for general assembly; fine pitch is used where higher clamp load or thinner walls matter. The pitch is the millimeters between two adjacent thread crests.
SAE thread pitch (TPI)
SAE threads are measured in threads per inch. UNC (coarse) and UNF (fine) are the two common series: a 3/8 UNC bolt is 16 TPI while 3/8 UNF is 24 TPI. Count the threads across one inch, or use a thread pitch gauge, to confirm before buying a matching nut.
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