Types of grading for high tensile bolts

High tensile bolts are specialized fasteners that are very important for the successful completion of a variety of projects. They are essential to the auto industry, for example, or in the construction and repair of industrial machines and components.

Choosing the right high tensile bolt is not a straightforward matter. There are several different grades of bolt – each one suited to specific purposes. Before selecting your fasteners, it will help to familiarize yourself with the different grades and what sets them apart.

What do the grades mean?

There are different systems of grading when it comes to bolts, which can cause a bit of confusion. The UK grades fasteners differently to the US – and you may sometimes see bolts with UK grading here. You might find bolts marked 8.8 or S, for example, while others are marked Grade 2 to 8, or marked with a series of three or six radial lines. When it comes to stainless steel bolts, we at Marsh Fasteners keep it simple. Since all stainless steel bolts are highly tensile, the exact rating of each one becomes a matter of the relative strength of the grade of steel used in their manufacture. Let’s run through the various grades that we carry.

High tensile stainless steel bolt grades

-   18-8: The numbers here indicate that the steel contains 18% chrome and 8% nickel, with a very small allowance for carbon (.08%). It is essentially another way of referring to 300 series stainless steel. The most common in this series are 303 and 304. Being the most corrosion-resistant and durable fasteners, these are well suited to freshwater aquatic environments (not to saltwater ones, however).

-   316: These bolts are recommended for harsh or marine (salt water) environments. They are more resistant to corrosion than 18-8. Bolts made of this material are used on boats, docks and piers.

-   305: This grade of steel was developed to improve the cold heading qualities of 18-8. Other than that, it is very much the same as 304 steel.

-   410: Bolts made of this steel are durable in most environments. 410 stainless steel is much harder than 18-8 but is not as resistant to corrosion. Choosing between 410 and 18-8 therefore involves a trade-off between hardness and rust-resistance.

Not sure which high tensile bolts to use for your project? Contact Marsh Fasteners and let us recommend the right fasteners for the job.

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