M6 Bolt Specifications
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
Every dimension, torque value, and thread specification for the M6 metric bolt in one reference card. M6 Bolt Specifications M6 is one of the most common fastener sizes in UK engineering, used for panel mounting, small motor brackets, and light machine assemblies.
| Property | Value | Standard |
|---|---|---|
| Nominal diameter | 6.0 mm | ISO 261 |
| Coarse pitch | 1.0 mm | ISO 261 |
| Fine pitch | 0.75 mm | ISO 261 |
| Tap drill (coarse, 75% engagement) | 5.0 mm | ISO 2306 |
| Tap drill (fine, 75% engagement) | 5.25 mm | ISO 2306 |
| Clearance hole - close | 6.4 mm | ISO 273 |
| Clearance hole - medium | 6.6 mm | ISO 273 |
| Clearance hole - coarse | 7.0 mm | ISO 273 |
| Hex head A/F (spanner size) | 10.0 mm | ISO 4014 |
| Hex head height | 4.0 mm | ISO 4014 |
| Socket head cap screw head dia | 10.0 mm | ISO 4762 |
| Socket head hex key size | 5.0 mm | ISO 4762 |
| Tensile stress area | 20.1 mm^2 | ISO 898-1 |
| Minimum tensile strength 8.8 | 800 MPa | ISO 898-1 |
| Minimum tensile strength 10.9 | 1040 MPa | ISO 898-1 |
| Proof load 8.8 | 11.3 kN | ISO 898-1 |
| Proof load 10.9 | 16.1 kN | ISO 898-1 |
| Torque dry, class 8.8 | 10 Nm | VDI 2230 |
| Torque dry, class 10.9 | 14 Nm | VDI 2230 |
| Torque dry, class 12.9 | 17 Nm | VDI 2230 |
M6 thread pitch
Standard M6 bolts use a 1.0 mm coarse pitch. Fine pitch M6 x 0.75 is used where vibration resistance matters or in thin-wall components, but it's less common off-the-shelf.
M6 tap drill size
For M6 x 1.0 coarse pitch with 75% thread engagement, drill 5.0 mm. For M6 x 0.75 fine pitch, drill 5.25 mm. Smaller drills give more engagement but increase tap breakage risk without meaningful strength gain.
M6 torque values
For a dry M6 property class 8.8 bolt, torque to 10 Nm. Class 10.9 takes 14 Nm, class 12.9 takes 17 Nm. All values assume dry threads (nut factor K=0.20). If threads are oiled, reduce torque by 20-25% to avoid over-stressing the bolt.
M6 spanner and hex key sizes
A standard M6 hex bolt (ISO 4014) has a 10 mm across-flats dimension, so it needs a 10 mm spanner or socket. An M6 socket head cap screw (ISO 4762) has a 10 mm head diameter and needs a 5 mm hex key (Allen key).
Related standards
- ISO 261 - ISO general-purpose metric screw threads: general plan
- ISO 273 - Fasteners: clearance holes for bolts and screws
- ISO 898-1 - Mechanical properties of fasteners made of carbon steel and alloy steel
- ISO 4014 - Hexagon head bolts, product grades A and B
- ISO 4762 - Hexagon socket head cap screws
- VDI 2230 - Systematic calculation of bolted joints
References
- ISO 261:1998 - ISO metric screw threads
- ISO 898-1:2013 - Mechanical properties of fasteners
- VDI 2230:2015 - Calculation of bolted joints
Frequently Asked Questions
What is the thread pitch of an M6 bolt?
A standard M6 bolt has a coarse thread pitch of 1.0 mm per ISO 261. The fine pitch version (less common) has a 0.75 mm pitch. If a drawing says M6 with no pitch specified, it means M6 x 1.0 coarse.
What is the tap drill size for M6?
For M6 x 1.0 coarse pitch with 75% thread engagement (the standard recommendation), drill 5.0 mm. For M6 x 0.75 fine pitch, drill 5.25 mm. These values give a good balance of thread strength and tapping ease.
What torque is an M6 bolt rated for?
For a dry M6 property class 8.8 bolt, the standard torque is 10 Nm. Class 10.9 takes 14 Nm, class 12.9 takes 17 Nm. Values are per VDI 2230 at 90% proof load with nut factor K=0.20. Reduce by 20-25% if threads are lubricated.
What spanner size fits an M6 bolt?
An M6 hex head bolt (ISO 4014) has a 10 mm across-flats (A/F) dimension, so you need a 10 mm spanner or socket. An M6 socket head cap screw uses a 5 mm hex key (Allen key).
What are M6 Bolt Specifications and why is it important for UK engineers?
The M6 Bolt Specifications provide detailed dimensions and standards for a common fastener size used in UK engineering. Engineers rely on these specifications to ensure correct fit, strength, and durability of components.
How do you differentiate between coarse pitch and fine pitch variants of the M6 bolt according to the specifications?
According to the M6 Bolt Specifications, the coarse pitch variant has a 1.0 mm pitch while the fine pitch version uses a 0.75 mm pitch. These differences affect threading density and engagement with materials.
What standards should UK engineers follow when choosing between clearance holes for an M6 bolt?
The M6 Bolt Specifications recommend ISO 273 standard clearance hole sizes of 6.4 mm (close fit), 6.6 mm (medium fit), and 7.0 mm (coarse fit) to ensure proper assembly and functionality.
Where can UK engineers find reliable suppliers for M6 bolts based on the specifications?
Engineers should consult reputable UK fastener suppliers such as Bolts Direct or Eurofasteners, who adhere to ISO standards outlined in the M6 Bolt Specifications.
What is the tensile stress area of an M6 bolt and why is it important?
The tensile stress area for an M6 bolt is 20.1 mm² according to the M6 Bolt Specifications. This measurement is important for calculating the bolt's strength and resistance against breaking under tension.
How does the availability and cost of M6 bolts vary in the UK market based on these specifications?
Availability and pricing of M6 bolts can fluctuate depending on demand, material costs, and adherence to ISO standards as specified. Engineers should check with suppliers like Fastenal or Ferguson for up-to-date inventory and price lists that conform to M6 Bolt Specifications.