Fasteners reference
M6 bolt reference: pitch, wrench, Allen key, and length
The useful measurements for identifying a common M6 fastener, including the fine-thread alternative and head-style differences.
Reviewed against GaugeFox data and the sources below · Updated August 4, 2026
What M6 × 1.0 means
M6 is the nominal major diameter: roughly 6 mm across the outside of the threads. The 1.0 is the pitch: one millimeter from one thread crest to the next.
M6 × 0.75 is a real fine-thread size with the same nominal diameter. If the shaft measures correctly but the fastener will not start in a known M6 nut, check the pitch before assuming either part is damaged.
| Feature | M6 × 1.0 | M6 × 0.75 |
|---|---|---|
| Nominal thread diameter | 6.00 mm | 6.00 mm |
| Thread spacing | 1.00 mm | 0.75 mm |
| Threads in 10 mm | About 10 | About 13.3 |
| Regular external hex | Commonly 10 mm | Commonly 10 mm |
The head style changes the tool
An M6 thread does not automatically mean a 10 mm wrench. That answer applies to a common regular external-hex head. An M6 socket-head cap screw has a cylindrical head with an internal hex recess and commonly takes a 5 mm Allen key.
| Head profile | Common Allen key |
|---|---|
| Socket-head cap | 5 mm |
| Button head | 4 mm |
| Flat / countersunk socket head | 4 mm |
Do not substitute 1/4-20 by eye
A 1/4-20 bolt is 6.35 mm in nominal diameter, only 0.35 mm larger than M6. Its thread spacing is 1.27 mm, which is the easier difference to see. The two threads are not interchangeable even when one starts into a worn or loose mating part.
Measure length from the correct face
For an external hex, button head, or socket-head cap screw, measure from the flat bearing surface under the head to the tip. For a flat countersunk screw, include the head and measure the full end-to-end length because the head sits in the countersink.
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 standard- ISO 261:1998 — ISO general purpose metric screw threadsInternational Organization for Standardization (opens in a new tab)
- ISO 4014:2022 — Hexagon head boltsInternational Organization for Standardization (opens in a new tab)
- ISO 4762:2004 — Hexagon socket head cap screwsInternational Organization for Standardization (opens in a new tab)
Use it at the bench
Put these references on your Android screen.
GaugeFox adds calibrated on-screen gauges, searchable nearby sizes, and a local Parts Bin to the reference data in this guide.