What is a high-tensile bolt?
The property class is shown on the bolt head and describes its strength: the first number relates to the tensile strength, and the second to the ratio of yield to tensile strength. Higher classes are made from medium-carbon or alloy steel that is quenched and tempered. High-tensile bolts must be used with matching nuts and washers, and tightened correctly so that the joint clamps reliably.
Listed manufacturers
No high-tensile bolt manufacturers are listed yet
We add manufacturers product by product. If your company makes high-tensile bolt, you can list it free and buyers reading this page will find you. Your details are reviewed before they appear.
List your companyHigh-Tensile Bolt or mild-steel bolt?
A mild-steel bolt is cheaper and suits light, general fixings. A high-tensile bolt carries much higher loads in the same size, which allows smaller joints, but it needs the right nut, correct tightening and care with coating because very high strength can make some bolts sensitive to hydrogen damage.
What to specify when you ask for a quote
- Property class and the standard it is made to.
- Thread size, pitch, length and head type.
- Material and heat treatment, and the hardness range.
- Coating: zinc plating, hot-dip galvanising or other, with the thickness and any baking for hydrogen relief on the highest classes.
- Matching nuts and washers, and the tightening method and torque.
- Test certificates for each lot, and the head marking and batch traceability.
Where it is used
- ConstructionStructural steel connections and bridges.
- AutomotiveEngine, chassis and wheel fasteners.
- Industrial MachineryMachine frames, couplings and flanges.
Frequently asked questions
What do the numbers on a bolt head mean?
They show the property class. For example, 8.8 means the nominal tensile strength is 800 megapascals and the yield is 80 percent of it. A higher number means a stronger bolt.
Can I use a high-tensile bolt with any nut?
No. The nut must be of a class suited to the bolt so that the thread does not strip before the bolt reaches its strength. Follow the standard for matching classes.
Why should high-strength bolts not be reused casually?
A bolt that was tightened close to its limit may have stretched or yielded, losing clamp force. In critical joints, follow the design guidance and replace bolts as it requires.
What is hydrogen embrittlement?
A loss of ductility in high-strength steel caused by hydrogen absorbed during plating or in service, which can lead to sudden failure. Coating processes for the highest classes need controls, so ask the supplier.