Identify a machine thread from measured diameter and pitch
The Thread Identifier compares your measurements with common metric thread sizes. For most threaded bolts and machine screws, nominal diameter is based on the outside diameter across the thread crests. Pitch is the distance from one thread crest to the next in metric systems. Both values matter: diameter alone does not uniquely identify a machine thread.
Measure before you enter values
- Clean rust, paint and debris from the threads.
- Measure the major diameter with a caliper, keeping the jaws square to the fastener axis.
- Measure pitch with a thread-pitch gauge whenever possible. If you do not have one, measure across several thread intervals and divide by the number of intervals rather than trying to measure a single crest-to-crest distance.
- Enter the measurements and use the closest match as a candidate, not final proof.
Why the closest number can still be wrong
Metric and inch threads can have similar diameters, and worn or plated threads can shift a caliper reading. A fastener that appears close to M8 is not automatically M8 × 1.25. Confirm the pitch and make sure a known mating part starts by hand without abnormal resistance.
Do not identify thread size from wrench size
The hex-head dimension is a separate feature from nominal thread diameter. A 13 mm wrench size does not mean the thread is M13. Fastener standards pair many different head dimensions with different thread diameters.
Current scope
The interactive matcher intentionally focuses on several common coarse metric sizes. It is not yet a complete ISO/Unified thread database and should not be used to force a near-match. FastenerBench will expand this tool with additional metric fine and Unified candidates only when the identification logic can keep false matches visible and understandable.
When exact identification matters most
Exact diameter and pitch are essential before tapping, installing a thread-repair insert or buying a replacement fastener for a loaded joint. If the original thread is damaged enough to distort the measurement, use an undamaged mating fastener, drawing, service information or a thread gauge as the primary reference.