When it comes to torque management and torque measurements, ensuring you use the correct torque values for bolts is essential to prevent common issues, such as overtightening and under-tightening.
Failure to follow torque measurement best practices can result in the bolt being either too loose or too tight, compromising the performance and safety of a mechanical assembly. This can potentially cause structural failure, unnecessary wear and tear and costly repairs and downtime if the assembly fails.
Understanding and applying the correct torque level when tightening bolts can help engineers improve the accuracy, safety and longevity of mechanical assemblies.
At Crane Electronics, we have more than five decades of experience in torque measurement and solutions. Our expertise and knowledge have helped us compile this handy guide to bolt torque values so that you can learn from our experience.
In this guide, we’ll explore the correct torque values for the most common size bolts that are used across a range of industries. We also highlight common mistakes engineers make when tightening torque bolts and the steps you can take to avoid them. But first, we look at the factors that can affect bolt torque values.
Factors that can affect bolt torque values
Achieving accurate bolt torque requires understanding several variables that influence how force is applied and transferred during tightening, to ensure safety, reliability and long-term joint integrity.
Understanding these variables is essential, as the torque specifications of bolts can be affected by a variety of circumstances, such as:
- Size: More torque is usually needed for larger bolts. This means that the torque required for an M6 bolt will differ from that for an M10 bolt. (Mx means a metric-sized bolt with a thread diameter of x mm)
- Bolt material: The material the bolt is made of affects the required torque. Stronger materials can cope with higher torque values.
- Condition of the thread: If the threads on the torque bolts are rusty or dirty, friction increases, which can lead to inaccurate torque application. Always ensure the thread and the overall bolt are clean to improve torque precision.
- Lubrication: Lubricated bolts have lower friction than dry bolts, so lower torque values are required.
- Thread pitch: Coarse threads have a different pitch than fine threads, which affects the torque required.
What are the torque values for bolts?
There is a range of bolt sizes that are regularly used across a range of industries, such as the automotive, aerospace, construction, manufacturing, power and energy and process industries. These include M6, M8, M10 and M16. Let’s take a closer look at the correct torque values for each of the common bolts, assuming they are the typical standard bolt grade for each size.
Torque for M6 bolts
M6 bolts are frequently used for smaller, less critical applications, but the correct torque values must still be applied. For an M6 bolt, the typical torque required value is approximately 9.6 Nm. Remember that factors such as lubrication and bolt material can affect torque. For example, a steel M6 bolt may have a different torque value than a stainless steel one.
Torque for M8 bolts
M8 bolts are commonly used in the automotive and construction industries. The approximate required torque for a standard grade M8 bolt is 24 Nm. Ensure that you follow the correct torque chart for your application to ensure precision.
Torque for M10 bolts
M10 bolts are often used in medium-duty applications and therefore require higher levels of torque. The approximate torque value for a standard steel M10 bolt is 46 Nm. If you are using M10 bolts made of other materials, such as stainless steel or aluminium, you’ll need to check your manufacturer’s guidelines for the correct torque values, as they may differ slightly.
Torque for M16 bolts
As a bolt that is used for heavy-duty industrial applications, it’s crucial that you follow torque measurement best practices. The correct approximate torque value for an M16 bolt is 210 Nm, this type of torque requires the right equipment to apply it accurately and safely. Failure to use the correct torque tools can weaken the bolt or make it more susceptible to damage.
Six common mistakes to avoid when applying torque
Precise torque measurements are crucial for safety and performance. Making common mistakes can cause material damage or complete component failure. The six most common torque management errors include:
1. Guessing the torque level
Not following the guidelines or torque measurement best practices can lead to under-tightening and overtightening, which can damage the bolt and increase its risk of failure. Use a calibrated torque wrench to ensure precise torque measurements and prevent loosening or damage. Find out why just guessing torque or assuming a joint is correctly fastened is a bad idea.
2. Treating all materials the same
Different bolts are made of various materials and each requires a different torque setting. Using a single torque value for all bolt materials can damage threads and compromise fastening performance. To prevent failures, check your torque chart or manufacturer’s guidelines for best practices.
3. Overtightening
You may think that tightening a bolt a little bit past the desired torque value will make the bolt stronger, but it can have the opposite effect. This is particularly true for bolts made of softer materials, as they can crack and weaken under excessive rotational load. Ensuring the correct amount of clamp load is critical for a safe and secure fastener.
4. Not considering lubrication
Lubricating bolts reduces friction, so they require less torque. You must consider this and reduce the torque values by around 10-20% for lubricated bolts. For example, adjust the torque for an M8 bolt from 24 Nm (dry) to around 19-21 Nm when lubricated to prevent over-tensioning. Find out more about the effect lubrication can have when applying torque.
5. Failing to recheck torque
Vibrations and wear and tear can cause bolts to loosen over time, which is why it’s crucial that you recheck torque at regular intervals. Several of Crane’s measurement-mode algorithms are designed to recheck torque after it has been initially applied. Click here to find out more about our torque measurement modes.
6. Using the wrong tools
Spanners or impact wrenches may appear capable, but they lack the precision and accuracy required for torque measurement. Ensure you always use the correct torque measurement tools and that they are regularly calibrated.
Why choose Crane for torque measurement?
At Crane, we’re the experts in torque measurement. We offer a wide range of products for torque measurement and tool auditing applications. From torque wrenches, torque transducers, torque testers, and software to joint simulators, test benches and data collectors. We have everything you need for effective torque management.
If you’d like more information about our torque measurement solutions or have any questions about our products and services, please contact us online, call us on +441455251488 or email sales@crane-electronics.com.