How Strong Are The Grade 8 Bolts, And Why Should You Use Them?

There are hardly a few fasteners that match the strength and reliability of Grade 8 bolts. This is why they are so common and play a critical role in various industries. Ranging from automotive and construction to heavy machinery and manufacturing, these Grade 8 bolts have been used everywhere. They are specified for high-strength applications. 

The bolts are commonly used in heavy manufacturing, such as tractor and truck fabrication. They are typically made of medium carbon alloy steel and plated in zinc for extra resilience. Grade 8 bolts can be identified by their flat, hexagonal head. This head is marked by six radial lines and occupies the highest position on the bolt-rating chart.

What Is a Grade 8 Bolt?

A Grade 8 bolt is a type of high-strength fastener. It is named after its SAE (Society of Automotive Engineers) grade classification. This is based on its mechanical properties. Therefore, “Grade 8” is short for “SAE J429 Grade 8.” The SAE J429 is one of the most common standards for inch fasteners, and grade 8 bolt is the highest grade.

Grade 8 bolts are made of medium-strength carbon or alloy steel. These can be finished in a variety of coatings and platings for added corrosion resistance and lubricity. The bolts are commonly used in heavy manufacturing like tractor and truck fabrication for instance. These can be identified through the flat, hexagonal head. It is marked by six radial lines and occupies the highest position on the bolt-rating chart. These bolts have their usage from automotive and construction to heavy machinery and manufacturing. These are specified for high-strength applications. 

Why Are These Bolts The Best Choice?

These bolts are the best choice for any kind of heavy-strength manufacturing because of a variety of reasons. These have been listed below:

  • The hardest and strongest hex bolt

A stainless steel bolt is weaker than a grade 8 bolt, even defying popular belief. In fact, as per the Society of American Engineers (SAE), grade 8 bolts are the strongest and hardest hex bolts. These are widely used in construction or the automotive industry. The carbon alloy bolts have a proof load of over 120,000 psi. At the same time, their stainless steel counterparts do not carry an indicative proof load. Moreover, the minimum strength of grade 8 bolts is around 130,000 psi. A stainless steel bolt, on the contrary, has a strength that does not exceed 90,000 psi. 

  • Available in all lengths and diameters

The super strong fastener is available in a wide variety of lengths. Depending on the particular use, one can choose it for various jobs considering the industry and the amount of stress and heavy loads it needs to bear. The extra length is obtained by extending the grip length, the thread length or both, based on the specific details of the application. The length of the fastener, which is measured by the distance between the bottom of the head and the end of the screw, is different from what is referred to in most industries as the ‘nominal length’. As far as the diameter is concerned, grade 8 bolts can be classified by the thread, shank or root diameter. 

  • Identifying a grade 8 bolt

If one needs to replace a fastener on one of the machines and suspects it is a grade 8 bolt, then one can easily find that out. Just check out the marking on the head of the bolt. A grade 8 bolt, as dictated by industry standards, will have six lines stamped into the head that point towards its centre. The metric equivalent of the lines is the number 10.9. If the bolt one is trying to identify is old and rusted, then there is a chance one cannot read the markings. In such a case, the best approach would be to search for the type of fasteners needed. One can always check that in the equipment’s manual.


High-strength bolts constitute high-strength applications. Using a Grade 8 bolt for anything less would never make sense. To speak frankly, it would be a waste of money. These bolts are typically used in military, heavy machinery, heavy trucks and aerospace.

For more information, visit Apzo Media

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