Most metric High Tensile (HT) nuts and bolts are produced in three grades, with the exception of mild steel.
Mild steel Grade 4.8 is the common starting grade for most threaded bar and square cup bolts (coach bolts).
Next is the starting High Tensile Steel Grade 8.8 which most bolts and H.T Hexagon Set Screws are manufactured to for general purpose use.
For more Tensile strength the next Grade up is 10.9, used in many fastener applications such as vehicle tow bars and suspension components.
The 3rd and strongest high Tensile Grade is 12.9, used in heavier fastener applications such as agricultural machinery and commercial vehicle components.
The high Tensile strength of a bolt is best protected by leaving the steel unplated. This doesn’t provide any form of corrosion protection apart from the natural oils created at point of manufacture.
If you are looking to replace a bolt and are unsure of what grade it is, you can often find the grade stamped on top of the head.
Arun Fasteners has a large range of high tensile, including 10.9 and 12.9 fasteners on our shelf. For a quote and availability call us on 01243 551484 or email email@example.com.