Fasteners reference
Metric, UNC, and UNF thread chart for common fasteners
Common thread diameters, Metric pitch, and Unified threads per inch for comparing nearby bolt and screw sizes.
Reviewed against GaugeFox data and the sources below · Updated August 29, 2026
Common metric coarse threads
| Thread | Nominal diameter | Pitch | Approximate TPI |
|---|---|---|---|
| M3 × 0.5 | 3.00 mm | 0.50 mm | 50.8 |
| M4 × 0.7 | 4.00 mm | 0.70 mm | 36.3 |
| M5 × 0.8 | 5.00 mm | 0.80 mm | 31.8 |
| M6 × 1.0 | 6.00 mm | 1.00 mm | 25.4 |
| M8 × 1.25 | 8.00 mm | 1.25 mm | 20.3 |
| M10 × 1.5 | 10.00 mm | 1.50 mm | 16.9 |
| M12 × 1.75 | 12.00 mm | 1.75 mm | 14.5 |
Common Unified coarse and fine threads
| Thread | Nominal diameter | TPI | Pitch equivalent |
|---|---|---|---|
| #6-32 UNC | 0.1380 in · 3.505 mm | 32 | 0.794 mm |
| #8-32 UNC | 0.1640 in · 4.166 mm | 32 | 0.794 mm |
| #10-24 UNC | 0.1900 in · 4.826 mm | 24 | 1.058 mm |
| #10-32 UNF | 0.1900 in · 4.826 mm | 32 | 0.794 mm |
| 1/4-20 UNC | 0.2500 in · 6.350 mm | 20 | 1.270 mm |
| 1/4-28 UNF | 0.2500 in · 6.350 mm | 28 | 0.907 mm |
| 5/16-18 UNC | 0.3125 in · 7.938 mm | 18 | 1.411 mm |
| 5/16-24 UNF | 0.3125 in · 7.938 mm | 24 | 1.058 mm |
| 3/8-16 UNC | 0.3750 in · 9.525 mm | 16 | 1.588 mm |
| 3/8-24 UNF | 0.3750 in · 9.525 mm | 24 | 1.058 mm |
Use the chart without forcing a near match
- Measure the major diameter across the outside thread crests.
- Match several crests against the pitch profile or count spaces over a known distance.
- Keep both systems visible when the diameter is close, such as M8 and 5/16 inch.
- Confirm with a known mating part by hand and stop immediately if it binds.
Reference trail
Sources and review method
These source pages identify the standards or industry references used for this guide. Full standards may require purchase. The guide is an identification aid, not a substitute for a calibrated inspection or the complete applicable standard.
Read the editorial standardUse it at the bench
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GaugeFox adds calibrated on-screen gauges, searchable nearby sizes, and a local Parts Bin to the reference data in this guide.