Metric Screw Thread Pitch: How to Measure It and Choose the Right Screw
Metric Screw Thread Pitch: How to Measure It and Choose the Right Screw
Two screws can have the same outside diameter and still refuse to fit the same nut. The missing measurement is often thread pitch—the distance between adjacent threads. Here is how to identify it correctly before buying a replacement screw, bolt or threaded component.
Same diameter.
Different pitch.
Different fit.
Measure the outside diameter, identify the pitch and confirm the threaded hole before ordering.
What is metric screw thread pitch?
Thread pitch (P) is the axial distance between equivalent points on adjacent thread turns, measured in millimetres for a standard single-start metric screw. For example, M6 × 1.0 means a nominal outside thread diameter of 6 mm and a pitch of 1.0 mm. The “M” identifies the ISO metric thread form; it does not specify the screw head or material.
A designation such as M4 × 0.7 × 10 mm commonly identifies a 4 mm nominal thread diameter, 0.7 mm pitch and 10 mm screw length. Length conventions depend on head style, so check the drawing or product description as well.
Visual guide: diameter versus pitch
Metric coarse thread pitch chart (M2 to M12)
For standard general-purpose ISO metric coarse threads, these are the commonly used nominal pitch values. A plain size such as “M6” often implies the coarse series in a general hardware context, but always verify the part specification when replacing an existing screw.
| Nominal thread size | Coarse pitch | Common designation | Typical application examples |
|---|---|---|---|
| M2 | 0.40 mm | M2 × 0.4 | Small electronics and instruments |
| M2.5 | 0.45 mm | M2.5 × 0.45 | Compact assemblies |
| M3 | 0.50 mm | M3 × 0.5 | 3D-printed parts and electronics |
| M4 | 0.70 mm | M4 × 0.7 | Brackets and general assemblies |
| M5 | 0.80 mm | M5 × 0.8 | Machinery and frames |
| M6 | 1.00 mm | M6 × 1.0 | Equipment and mounting |
| M8 | 1.25 mm | M8 × 1.25 | Fixtures and structural brackets |
| M10 | 1.50 mm | M10 × 1.5 | Machinery and fabricated assemblies |
| M12 | 1.75 mm | M12 × 1.75 | Industrial equipment |
Values follow the ISO metric coarse series. This table is for pitch identification, not a tapping-drill or tightening-torque specification.
How to measure screw pitch in four steps
Step 1 — Measure the outside thread diameter
Use a vernier or digital caliper across the outermost thread crests. A screw close to 4 mm nominal diameter is likely an M4 candidate; actual measured values can be slightly below nominal because of manufacturing tolerances. Do not use the head diameter to identify the thread.
Step 2 — Match a metric thread pitch gauge
Open a metric gauge leaf marked with a candidate pitch (for example, 0.7). Place the toothed edge along a clean, undamaged section of the external thread. The teeth should seat evenly along several turns without visible mismatch or rocking. Try adjacent sizes if the fit is unclear.
Step 3 — Read the pitch and cross-check the chart
If the diameter is approximately 4 mm and the gauge reads 0.7 mm, the likely designation is M4 × 0.7. For an M8 screw, 1.25 mm indicates the common coarse series, while 1.0 mm is a commonly specified finer option.
Step 4 — Confirm the mating thread before assembly
Verify that the nut, insert or tapped hole has the same thread specification. Start engagement by hand; do not force a screw that binds. If the application is critical, a fit test alone is not a substitute for checking the specified thread tolerance and material requirements.
What if you do not have a pitch gauge?
For a reasonably long, clean thread, measure a known axial distance spanning several full thread intervals and divide that distance by the number of intervals. For example, 10 intervals occupying 8 mm gives an estimated pitch of 0.8 mm. A caliper is helpful, but this method is approximate on short or damaged threads. For an exact replacement, use a gauge or a known-good reference fastener.
Metric coarse vs fine thread: what changes?
Coarse and fine refer to thread spacing for the same nominal diameter. Finer threads have a smaller pitch, so they advance a shorter axial distance per turn. This can be useful for adjustment or certain engineered joints, but fine pitch is not a universal cure for loosening under vibration. Proper joint design, preload and locking method still matter.
| Feature | Coarse metric thread | Fine metric thread |
|---|---|---|
| Pitch at a given diameter | Larger spacing | Smaller spacing |
| Example at M8 | M8 × 1.25 | M8 × 1.0 |
| Assembly | Common general-purpose choice; often more tolerant of minor dirt/damage | Requires closer attention to matching and cleanliness |
| Axial movement per turn | More | Less, useful for finer adjustment |
| Interchangeability | Not interchangeable with a different pitch, even when nominal diameter matches | |
Five common thread-identification mistakes
| Mistake | Why it matters | Better approach |
|---|---|---|
| Matching by head size | Different thread sizes can use similar heads | Measure external thread diameter |
| Assuming all M8 screws have 1.25 mm pitch | M8 × 1.0 is also used | Gauge the existing screw or check the drawing |
| Forcing a screw into a nut | May damage both threads | Stop if it does not start freely by hand |
| Confusing pitch with TPI | Metric uses mm; imperial commonly uses threads per inch | Use the correct gauge and designation |
| Assuming a pitch gauge proves thread quality | It identifies spacing, not all tolerance limits | Use appropriate GO/NO-GO gauging for inspection |
Useful OnlyScrews tools and metric screws
The following seven Shopify product pages were rechecked on 29 October 2026; each was active with positive reported inventory at the time of review. Check current stock and variant specifications before ordering. Product links below are direct links, not unverified search pages.
Frequently asked questions
What is the standard thread pitch for M3, M4, M5 and M6?
Common ISO metric coarse pitches are M3 × 0.5, M4 × 0.7, M5 × 0.8 and M6 × 1.0 mm.
Can an M8 × 1.0 screw fit an M8 × 1.25 nut?
No. Both have the same nominal diameter, but the thread spacing differs. Do not force them together.
How do I know if a screw is metric or imperial?
Check the measured diameter, gauge the pitch and compare the designation. Metric gauges read millimetres; imperial gauges often read threads per inch (TPI).
Does a caliper measure thread pitch accurately?
A caliper can estimate pitch across several full intervals, but a correctly matched pitch gauge is more practical for identification. Inspection-grade tolerances require appropriate dedicated gauges.
Is coarse pitch always better than fine pitch?
No. Coarse pitch is common for general assembly; fine pitch can suit specific adjustment or engineered joint requirements. The drawing and mating part determine the correct choice.
What information should I send when requesting a replacement screw?
Send a clear photo, measured diameter, thread pitch, length, head and drive type, material/finish, and—if possible—the part drawing or an undamaged sample.
Related OnlyScrews guides
Need the other measurements too? Read How to Measure the Diameter of a Screw, How to Measure Screw Length and M2 vs M3 vs M4: Which Screw Size Should You Choose?.
Metric thread identification workflow
Technical references
- ISO 261:1998 — General plan for ISO metric screw threads (ISO site confirms current status, last reviewed 2024).
- ISO 965-1:2026 — Metric screw thread tolerances (current edition, published April 2026).
- Metric coarse thread reference table (pitch values cross-checked against ISO 261).
- Thread pitch measurement and common coarse/fine comparisons.
- OnlyScrews metric pitch gauge product description (leaf-gauge usage and materials).