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ASTM F3125 vs A325 Bolts – What’s the Difference

ASTM F3125 vs A325 Bolts

Bolts are a critical component of any construction project. They play a vital role in providing the necessary strength and durability to the structure. However, selecting the correct type of bolt is crucial, as it directly affects the safety and longevity of the building. Two common types of bolts are ASTM F3125 and A325. In this post, we will compare the two and help you decide the best choice for your project.

First, let’s understand the differences between ASTM F3125 and A325 bolts. A325 bolts are a type of high-strength bolt commonly used in structural steel connections. On the other hand, ASTM F3125 is a standard covering different bolts, including A325 and other high-strength bolts, such as A490 and F1852. Therefore, ASTM F3125 bolts can be either A325 or high-strength bolts.

While both bolts offer excellent tensile strength, there are some differences in their mechanical properties. A325 bolts have a lower yield and higher tensile strength than ASTM F3125 bolts. This makes them ideal for high-load applications like bridges or high-rise buildings. However, if your project requires a higher level of corrosion resistance, then ASTM F3125 bolts are the best choice, as they offer several different coatings that can resist corrosion.

Another advantage of using ASTM F3125 bolts is that they have a more comprehensive range of diameters and lengths than A325 bolts. This means you can find the correct bolt size for your project, which is essential for proper installation and structural integrity.

Regarding installation, there are also differences between ASTM F3125 and A325 bolts. A325 bolts use a heavy hex structure, while F3125 bolts come in either a heavy hex or a hex structure. The installation process for both bolts is quite similar. However, F3125 bolts can be installed using either a hex wrench or a torque wrench, making them more versatile and easier to install.

Finally, it’s worth noting that ASTM F3125 bolts are a newer standard and have replaced the A325 and A490 standards. This means that F3125 bolts have undergone more recent testing and standardization than A325 bolts, making them a more modern and updated option.

Difference Between ASTM F3125 and A325

The main difference between ASTM F3125 and A325 is that ASTM F3125 is a newer specification that covers a broader range of fasteners, while A325 is an older specification that only covers bolts. Both specifications are for high-strength structural bolts, but ASTM F3125 includes several grades of bolts that A325 does not cover. Additionally, the two specifications have different requirements for thread length and head markings.

Which Specification should be used?

The appropriate Specification to use will depend on the application. If the fasteners need to meet the requirements of both specifications, then ASTM F3125 should be used. However, if only the requirements of A325 are required, then it is acceptable to use that Specification.

What are the Grades of Bolts Covered by ASTM F3125?

Four bolts are covered by ASTM F3125: A, B, C, and D. Grade A bolts have the lowest strength, while Grade D bolts have the highest power. Grade C bolts fall in between these two extremes.

What are the Requirements for Thread Length?

The minimum thread length required by both specifications is 1 1/2 times the diameter of the bolt shank. For example, if the bolt has a diameter of 1/2 inch, then the minimum thread length would be 3/4 inch. The size of the bolt shank determines the maximum thread length.

What are the Requirements for Head Markings?

Both specifications require that the manufacturer’s name or trademark be stamped on the head of each bolt. Additionally, ASTM F3125 requires that the grade be stamped on the head of each bolt, while A325 only requires this for Grade C and D bolts.


When selecting the right bolt for your project, it’s essential to consider the application, mechanical properties, installation process, and standards. While ASTM F3125 and A325 bolts offer excellent strength and durability, their mechanical properties, corrosion resistance, and installation methods differ. We hope this post has helped you understand the differences between the two and make an informed decision for your next project. Regardless of which bolt you choose, ensure that it meets the requirements and standards for safety and longevity.

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