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Torque values for metric hex bolts in property classes 8.8, 10.9, and 12.9. These bolt torque values are for dry, unlubricated steel bolts with a nut factor K = 0.20, which corresponds to roughly 70% of proof load per ISO 898-1. The chart runs from M3 to M39. Lubricated bolts (K = 0.15) require roughly 25% less torque. Always confirm torque specs against the fastener manufacturer's data for critical applications.
| Size |
Pitch (mm) |
8.8 (Nm) |
10.9 (Nm) |
12.9 (Nm) |
| M3 | 0.5 | 1.3 | 1.8 | 2.1 |
| M4 | 0.7 | 3.0 | 4.3 | 5.0 |
| M5 | 0.8 | 5.9 | 8.4 | 9.8 |
| M6 | 1.0 | 10 | 14 | 17 |
| M8 | 1.25 | 25 | 35 | 41 |
| M10 | 1.5 | 49 | 69 | 81 |
| M12 | 1.75 | 85 | 120 | 140 |
| M14 | 2.0 | 135 | 190 | 225 |
| M16 | 2.0 | 210 | 295 | 345 |
| M18 | 2.5 | 285 | 400 | 470 |
| M20 | 2.5 | 405 | 570 | 670 |
| M22 | 2.5 | 550 | 780 | 910 |
| M24 | 3.0 | 690 | 970 | 1140 |
| M27 | 3.0 | 1050 | 1470 | 1720 |
| M30 | 3.5 | 1400 | 1960 | 2300 |
| M33 | 3.5 | 1920 | 2660 | 3110 |
| M36 | 4 | 2470 | 3420 | 3990 |
| M39 | 4 | 3200 | 4420 | 5170 |
M33, M36 and M39 torque values
The last three rows of the chart are calculated with the formula T = K x d x F, using a nut factor K of 0.20 and a preload F of 70% of the bolt's proof load. For an M36 class 8.8 bolt the stress area is 817 mm2 and the proof stress is 600 MPa, so the proof load is 490 kN, the preload is 343 kN and the torque is 0.20 x 0.036 x 343140 = 2471 Nm, rounded to 2470 Nm in the chart. The M3 to M30 rows work out at 68% to 74% of proof load on the same basis.
There are no rows above M39. ISO 898-1 defines property classes 8.8, 10.9 and 12.9 for coarse thread bolts up to M39 only, so a torque figure for M42 or larger depends on the material standard the bolt was actually made to. Use the bolt maker's data or a joint calculation for those sizes.
What the property class numbers mean
The first number is the nominal tensile strength in hundreds of megapascals, and the second is the ratio of yield to tensile strength. Class 8.8 is 800 MPa nominal tensile with a yield of 0.8 times that, 640 MPa. The minimum values a bolt has to meet are slightly different from the nominal ones, and class 8.8 has two sets depending on diameter:
Property class |
Nominal tensile (MPa) |
Minimum tensile (MPa) |
Nominal yield (MPa) |
Minimum yield (MPa) |
Proof stress (MPa) |
|---|
| 8.8, up to M16 | 800 | 800 | 640 | 640 | 580 |
| 8.8, above M16 | 800 | 830 | 640 | 660 | 600 |
| 10.9 | 1000 | 1040 | 900 | 940 | 830 |
| 12.9 | 1200 | 1220 | 1080 | 1100 | 970 |
How to use the metric bolt torque chart
Find the bolt size in the left column, then read across to the property class stamped on the bolt head. Property class 8.8 is the most common grade for general engineering. Class 10.9 is used in automotive and high-strength structural joints. Class 12.9 is the highest standard grade, typically socket head cap screws.
These values assume clean, dry threads with no lubricant. If you're using oil, grease, or thread paste, reduce the torque by 20-30% or use the K-factor method: T = K x d x F, where T is torque in Nm, d is nominal diameter in metres, and F is the target clamp force in newtons.
For flange bolts or bolts with prevailing torque locknuts, add the prevailing torque to the values shown. Always torque in a star pattern on multi-bolt flanges.
Related standards
- ISO 898-1 - Mechanical properties of fasteners made of carbon steel and alloy steel (bolts, screws, studs)
- ISO 898-2 - Mechanical properties of fasteners (nuts with specified proof load)
- VDI 2230 - Systematic calculation of bolted joints
- BS EN ISO 4014 - Hexagon head bolts, product grades A and B
- BS EN ISO 4762 - Hexagon socket head cap screws
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Frequently Asked Questions
What torque should I use for an M10 8.8 bolt?
An M10 property class 8.8 bolt should be torqued to 49 Nm with dry, unlubricated threads (K=0.20). If the threads are oiled, reduce to about 37 Nm.
What do bolt property classes 8.8, 10.9 and 12.9 mean?
The first number multiplied by 100 gives the minimum tensile strength in MPa. The second number is the ratio of yield to tensile strength. So 8.8 means 800 MPa tensile, 640 MPa yield. 10.9 means 1040 MPa tensile, 940 MPa yield. 12.9 means 1220 MPa tensile, 1100 MPa yield.
Should I lubricate bolts before torquing?
It depends on the application. Lubrication lowers the nut factor from about 0.20 (dry) to 0.15 (oiled) or 0.12 (MoS2 paste), meaning you need less torque for the same clamp force. If you lubricate, you must reduce the torque setting accordingly or you'll over-stress the bolt.
What does the Metric Bolt Torque Chart provide information about?
The Metric Bolt Torque Chart provides torque values for metric hex bolts in property classes 8.8, 10.9, and 12.9, suitable for dry, unlubricated steel bolts tightened to 90% of proof load according to ISO 898-1 standards.
How do lubricated bolts differ from dry bolts in the Metric Bolt Torque Chart?
Lubricated bolts require roughly 25% less torque than dry bolts as indicated by the chart, with a nut factor K = 0.15 compared to 0.20 for dry conditions.
What factors should be considered when choosing values from the Metric Bolt Torque Chart?
When selecting torque settings from the chart, engineers must confirm specifications against the fastener manufacturer's data, especially for critical applications where precise tightening is important.
Which standards does the Metric Bolt Torque Chart adhere to?
The Metric Bolt Torque Chart adheres to ISO 898-1 standards for determining proper torque values for metric hex bolts in various property classes.
Are there UK suppliers listed on mlc.org.uk that provide fasteners referenced by the Metric Bolt Torque Chart?
While specific supplier names aren't provided, engineers can find information about UK suppliers of fasteners compatible with the chart's standards and torque settings on mlc.org.uk.
How frequently is the Metric Bolt Torque Chart reviewed or updated for accuracy?
The Metric Bolt Torque Chart is verified by a Supply Chain Analyst, as indicated by a recent verification date (April 2026), ensuring its information remains accurate and up-to-date according to industry standards.
What is the cost implication of using incorrect torque settings based on the Metric Bolt Torque Chart?
Using incorrect torque settings can lead to over-tightening or under-tightening bolts, which may result in structural failures or component damage, potentially leading to costly repairs and safety issues. Always refer to the chart for accurate values to avoid these risks.
What is the torque for an M36 bolt?
An M36 class 8.8 bolt with dry threads takes about 2470 Nm, class 10.9 about 3420 Nm and class 12.9 about 3990 Nm, at a nut factor of 0.20 and 70% of proof load.
Why is there no torque value for M42 and larger bolts?
ISO 898-1 defines property classes 8.8, 10.9 and 12.9 for coarse thread bolts up to M39 only. Above that the strength depends on the material standard the bolt was made to, so use the bolt maker's data.