How to Measure Thread Pitch
Accurate pitch measurement is the key to identifying unknown bolts and choosing the right tap or die. Use calipers and a pitch gauge, then verify with our tools.
Using a thread pitch gauge
Pitch gauges have blades marked with metric pitch (mm) or TPI. Hold the blade against the thread; when it meshes without gap, the marked value is your pitch or TPI. Try both metric and imperial blades if unsure.
Measuring pitch with calipers
Measure the distance from the first thread crest to the 11th crest (so 10 full pitches). Divide by 10 to get pitch in mm. For TPI, measure 1 inch along the axis and count the number of crests in that length.
| Method | Metric | Imperial (TPI) |
|---|---|---|
| Pitch gauge | Match mm blade | Match TPI blade |
| Caliper | Distance over N crests ÷ N = pitch (mm) | Count crests per inch |
Identifying the thread
Once you have diameter and pitch (or TPI), use our Thread Identifier to get likely designations (e.g. M6 x 1.0 or 1/4-20). Convert between pitch and TPI with our Thread Pitch to TPI Converter.
FAQ
How do you measure thread pitch with calipers?
Measure the distance over 10 thread crests (or more), then divide by the number of threads to get pitch. For TPI, count threads per inch along the axis.
What tool measures thread pitch?
A thread pitch gauge has blades for metric (mm) and imperial (TPI). Match the blade to the thread; the marked value is the pitch or TPI.
How do I use measured pitch to identify a bolt?
Enter the measured diameter and pitch (or TPI) into our Thread Identifier tool to get likely thread designations like M6 or 1/4-20.
Related
Tools: Thread Identifier, Thread Pitch to TPI Converter
Charts: Universal Screw & Bolt Size Chart, Screw Size Chart
Guide: What Is TPI