Metric Thread Pitch Guide: M2 to M20 Coarse Threads
Thread pitch is one of the easiest fastener details to overlook because many everyday metric screws use the standard coarse series. Pitch is the distance, in millimetres, from.
Thread pitch is one of the easiest fastener details to overlook because many everyday metric screws use the standard coarse series. Pitch is the distance, in millimetres, from one thread crest to the next. An M3 coarse thread commonly uses a 0.5 mm pitch, while an M6 coarse thread commonly uses 1.0 mm. A wrong pitch can start into a mating thread and then bind or damage it, so verification matters.
Metric thread systems use a combination of nominal diameter and pitch. The M-size identifies the nominal diameter; the pitch identifies how closely the threads are spaced. Coarse pitch is common for general-purpose fastening, while fine pitch may be chosen for specific design, adjustment, strength or packaging reasons.
Quick answer: Thread pitch is one of the easiest fastener details to overlook because many everyday metric screws use the standard coarse series.
What to know about metric thread pitch guide
Coarse pitch
Coarse threads are widely stocked and generally more tolerant of dirt, minor damage and quick assembly. They are the normal starting point for general mechanical work.
Fine pitch
Fine threads place more threads within a given axial distance. They can be useful where adjustment, reduced thread depth or specific engineering requirements matter, but they must match the mating thread exactly.
Pitch measurement
A metric thread pitch gauge is the quickest way to identify pitch. If a gauge is unavailable, measure the distance across several thread peaks and divide by the number of intervals to reduce measurement error.
Mating components
A bolt and nut must share both nominal diameter and pitch. M6×1.0 and M6×0.75 are both M6 threads but they are not interchangeable.
How to choose the right fastener
- Use the drawing or BOM first: If the assembly documentation specifies pitch, follow it rather than relying on a sample fastener.
- Use a thread gauge: A gauge makes it much easier to distinguish nearby pitches.
- Check existing nuts and tapped holes: Do not force a fastener that becomes tight after only a turn or two.
- Be careful with replacement parts: Equipment manufacturers may use fine threads in places where coarse threads are more common in general retail.
- Store coarse and fine threads separately: Clear bin labels reduce accidental cross-threading during maintenance.
Quick comparison
| Metric size | Common coarse pitch | Typical notation |
|---|---|---|
| M2 | 0.40 mm | M2×0.40 |
| M2.5 | 0.45 mm | M2.5×0.45 |
| M3 | 0.50 mm | M3×0.50 |
| M4 | 0.70 mm | M4×0.70 |
| M5 | 0.80 mm | M5×0.80 |
| M6 | 1.00 mm | M6×1.00 |
| M8 | 1.25 mm | M8×1.25 |
| M10 | 1.50 mm | M10×1.50 |
| M12 | 1.75 mm | M12×1.75 |
| M16 | 2.00 mm | M16×2.00 |
| M20 | 2.50 mm | M20×2.50 |
A practical ordering workflow
Before placing an order for metric thread pitch guide, turn the application into a short specification. Start with the mating thread and physical envelope, then confirm the head or drive, material and finish. If the fastener is part of a loaded, vibrating, outdoor or frequently serviced joint, add the relevant mechanical, corrosion and maintenance requirements before choosing a SKU.
For repeat purchases, record the exact approved description in your bill of materials or purchasing system instead of relying on a photograph or an old sample. That record should include the dimensions that control fit, the material or property class, the finish, and any standard or certificate requirement. This makes replacement orders easier to compare and helps prevent accidental substitutions.
When a dimension, torque value, strength requirement or corrosion condition is safety-critical, use the applicable engineering drawing, current standard and manufacturer documentation as the final authority. Catalogue guidance is useful for narrowing choices, but it should not override the requirements of the actual joint.
How to verify the specification before ordering
Make the first verification on the actual assembly or approved drawing. For use the drawing or bom first, if the assembly documentation specifies pitch, follow it rather than relying on a sample fastener. For use a thread gauge, a gauge makes it much easier to distinguish nearby pitches. Do not assume that an older fastener removed from the machine is still the approved specification; previous repairs may have introduced substitutions.
If the part is being introduced into production, buy a small validation quantity before committing to a large lot. Check thread engagement by hand, seating of the head or nut, tool clearance, surface marking, interference with nearby parts and the condition of the mating thread after assembly. Where traceability or mechanical properties matter, compare received markings and documents with the purchase specification. This small verification step is especially useful when changing suppliers, materials, finishes or dimensional standards.
Common mistakes to avoid
- Assuming all fasteners with the same diameter have the same pitch.
- Using thread count per inch terminology for metric pitch without converting correctly.
- Trying to repair a mismatched thread by applying more torque.
- Measuring only one thread interval with a worn ruler or caliper.
- Mixing fine- and coarse-thread nuts in the same unlabelled storage bin.
Recommended products and categories
You can continue from this guide by viewing M3 stainless-steel hex nut, M6 stainless-steel hex nut and metric hex nuts.
Technical references
The following independent technical references are useful for checking terminology, standards and engineering background. They are provided for reference and do not imply endorsement of any product sold on this site.
Frequently asked questions
What is the pitch of an M3 screw?
The common ISO coarse pitch for M3 is 0.50 mm.
What is the pitch of an M6 screw?
The common ISO coarse pitch for M6 is 1.00 mm.
Is a lower pitch number a finer thread?
Yes. For the same nominal diameter, a smaller pitch value means the thread crests are closer together.
Can a coarse-thread bolt fit a fine-thread nut of the same M-size?
No. The nominal diameter may match, but the different helix spacing prevents proper engagement and can damage both parts.
Related reading
Final buying checklist
- Confirm the nominal thread diameter and thread pitch.
- Confirm the required length and the correct head-to-tip measuring method.
- Check head style, drive style and installation-tool access.
- Match material and finish to the service environment and mating materials.
- Check strength, locking, documentation and application limits where they matter.
Pitch should be treated as part of the thread identity. When you record diameter and pitch together, replacements become safer, faster and far less likely to damage a tapped hole or nut.
Ready to select a part? Browse our Screws, Nuts & Bolts catalogue and filter by thread size, material, finish, head style and drive type.