Quick & Easy: How to Identify High Tensile Bolts
When your project demands extra strength – whether it's for a vehicle upgrade or heavy machinery – high tensile bolts are a must. At AIMS Industrial, we’re here to help you understand what to look for in a fun and easy way.
Understanding Bolt Grades
Bolt grades indicate the strength and durability of the bolt. In Australia, you will commonly encounter these grades:
|
Grade |
Description |
|
8.8 |
Medium carbon steel, quenched and tempered |
|
10.9 |
Alloy steel, quenched and tempered for extra strength |
|
12.9 |
Alloy steel with the highest tensile strength |
How to Identify High Tensile Bolts
Look for the grade markings stamped on the bolt head – these numbers tell you the bolt’s strength:
- 8.8: Marked with "8.8"
- 10.9: Marked with "10.9"
- 12.9: Marked with "12.9"
Choose the Right Bolt for Your Application
Not every project requires the same level of strength. Here are some of our top picks available at AIMS Industrial:
- Metric Hex Bolt - Grade 8.8 High Tensile Zinc Finish – Ideal for many structural applications.
- Bumax 10.9 Stainless Steel High Tensile Hex Bolt – Perfect for projects needing extra corrosion resistance.
- M20 x 24 x 80 Socket Head Shoulder Screw Plain High Tensile G12.9 – The top choice when maximum strength is essential.
Safety, Time and Money
Selecting the right high tensile bolt is crucial for the safety and longevity of your projects. Always check the bolt head for grade markings and choose the one that best fits your application. Explore our full range of high-quality fasteners on our Bolts Collection for more options.
For a comprehensive guide CLICK HERE
At AIMS Industrial, we make sure you have the right tools for every project. Happy bolting!
People Also Ask — High-Tensile Bolt Identification
Q: How can I tell if a bolt is high-tensile?
The quickest way is to read the head markings. Metric high-tensile bolts carry a property class number stamped on the head, such as 8.8, 10.9 or 12.9 — the higher the number, the stronger the bolt. Imperial bolts use radial lines on the head, where more lines indicate a higher grade. A bolt with no markings is generally a low-grade commercial fastener and should not be assumed to be high-tensile. So before relying on a bolt for a structural or high-load joint, check the head: a clear property class number or a set of radial lines tells you it is a graded, high-tensile fastener rather than a general-purpose one.
Q: What do the numbers like 8.8, 10.9 and 12.9 mean?
These are metric property class markings, and they encode the bolt's strength. The first number relates to the bolt's tensile strength and the second to its yield strength as a proportion of tensile, so a higher pair of numbers means a stronger, harder bolt. In practice, 8.8 is the common high-tensile grade for general engineering, 10.9 is used for more demanding joints, and 12.9 is among the highest standard grades for the most heavily loaded applications. The system lets you compare bolts at a glance — a 10.9 is stronger than an 8.8 — which is why matching the property class to the joint's requirement matters.
Q: How do imperial bolt grade markings work?
Imperial bolts show their grade through radial lines stamped on the head rather than numbers. No lines indicate a low-grade bolt, three radial lines indicate a common medium-high grade, and six radial lines indicate a higher grade again — more lines means a stronger bolt. Because the markings differ from the metric number system, it is important not to confuse the two: an unmarked head is not the same as a graded metric bolt. When working in imperial, count the radial lines to read the grade, and confirm against the supplier's specification if the joint is critical. Mixing up imperial and metric grade systems is a common and avoidable error.
Q: Why does using the correct bolt grade matter?
Bolt grade determines how much tension and shear a fastener can safely carry. Using a bolt that is too low a grade in a high-load joint risks the bolt yielding or failing, which in structural, lifting or machinery applications can be dangerous. Conversely, the grade affects the correct tightening torque, so fitting the wrong grade and torquing it as if it were another can over- or under-stress the joint. Matching the bolt's property class or grade to the engineering requirement — and torquing it accordingly — is what keeps the joint safe and reliable. When a joint is critical, always confirm the specified grade rather than substituting whatever is on hand.
Q: Can I substitute a higher-grade bolt for a lower one?
It is often acceptable to use a higher-grade bolt where a lower grade is specified, since the stronger bolt has greater load capacity — but it is not automatic. Higher-grade bolts are harder and can be more brittle, the correct tightening torque changes with grade, and some applications deliberately specify a particular grade for reasons such as controlled failure or ductility. Going the other way — substituting a lower grade where a higher one is called for — should never be done, as it under-rates the joint. The safe rule is to match the specified grade where you can, and only step up after confirming the higher grade and its torque suit the application.
For champion, see our champion range stocked across Australia.
Need bumax? Browse the AIMS range at bumax.