...

The different grades of bolts

Table of Contents
Are you confused by the different bolt grades? Don’t worry, I’m Monica Song, have 16 Years experience in fasteners and today I’m going to break down the different bolt grades for you. If you have questions about SAE, metric, or ASTM standards, I’m going to answer them right here. Bolts are classified by their strength and material properties. Common SAE grades are 2 (low strength), 5 (medium strength), and 8 (high strength). Metric grades include 5.8, 8.8, 10.9, and 12.9, with increasing strength. ASTM grades like A307, A325, and A490 also exist, suited for various applications. Intrigued? Let’s dive deeper into the world of bolt grades and discover their unique characteristics and applications.

What are Bolt Grades, Tensile Strength, and Yield Strength?

Bolt grades describe the material and mechanical properties of bolts, particularly their tensile and yield strength. These grades help in choosing the right bolt for the required strength, durability, and environmental conditions. Tensile Strength: The maximum load a bolt can handle without breaking. For example, a Grade 8 bolt has a higher tensile strength than a Grade 2 bolt, making it suitable for more demanding applications. Yield Strength: The load at which a bolt begins to deform plastically. After this point, the bolt will not return to its original shape. HYou want high yield strength if you need a bolt to maintain its form under heavy loads. Understanding these properties ensures that you select the correct bolt grade for your application, ensuring safety and performance.
grades of bolts

What are the Different Bolt Grade Standards?

In the realm of bolts, three primary classification systems exist: SAE (Society of Automotive Engineers), Metric, and ASTM (American Society for Testing and Materials). Each system has its distinct marking and usage criteria.

SAE Grades

The SAE grading system primarily applies to imperial bolts and uses radial lines on the bolt head to denote different strength levels.
    1. SAE Grade 2: Made of low carbon steel, these bolts are suitable for general purposes with a tensile strength of approximately 60,000 psi (about 414 MPa). They have no head markings and are perfect for light-duty applications like household fixtures, furniture assembly, and non-critical automotive and agricultural equipment parts.
    1. SAE Grade 5: Composed of medium carbon steel, quenched, and tempered, these bolts boast a tensile strength of about 105,000 psi (around 724 MPa). Marked with three radial lines, they are ideal for medium-strength requirements such as automotive chassis, agricultural equipment, and machinery.
    1. SAE Grade 8: These high-strength alloy steel bolts, also quenched and tempered, feature a tensile strength of around 150,000 psi (approximately 1034 MPa). Marked with six radial lines, they are designed for high-stress environments like engine parts, suspension systems, and heavy-duty structural connections.
SAE Grades

Metric Grades

Metric bolts are graded by their material strength and are often marked directly on the bolt head with numbers such as “8.8”, “10.9”, and “12.9”.
    1. Class 8.8: Made from medium carbon steel and heat-treated to achieve a tensile strength of 830 MPa, these bolts are suitable for general strength applications. They are marked with “8.8” and commonly used in general machinery, automotive parts, and light steel structures.
    1. Class 10.9: High-strength alloy steel bolts with a tensile strength of 1040 MPa. Marked with “10.9”, they are used in high-strength applications such as structural connections, heavy machinery, and automotive components requiring high strength.
    1. Class 12.9: The highest strength bolts made from alloy steel, boasting a tensile strength of 1220 MPa. Marked with “12.9”, they are suitable for extremely high-strength requirements like aerospace, high-performance racing, and heavy engineering machinery.
Metric Grades

ASTM Grades

ASTM standards provide comprehensive specifications and performance requirements for bolts, using a combination of letters and numbers to denote different grades.
    1. A307: These low carbon steel bolts, with a tensile strength of around 60,000 psi (about 414 MPa), are suitable for general-purpose low-stress applications. Marked with “A307”, they are commonly used in general structural connections, light steel structures, and furniture manufacturing.
    1. A325: High-strength bolts with a tensile strength of 120,000 psi (approximately 827 MPa), marked with “A325”. They are ideal for high-stress structural applications like bridges, high-rise buildings, and heavy machinery.
    1. A490: These alloy steel bolts have a tensile strength of 150,000 psi (around 1034 MPa) and are marked with “A490”. They are used in ultra-high-stress applications such as skyscrapers, large-span bridges, and critical aerospace structures.
ASTM Grades

Is a grade 8.8 bolt stronger than a 8 grade?

No, A Grade 8 bolt is stronger than a Grade 8.8 bolt. While Grade 8.8 is a metric standard with a tensile strength of 800 MPa (116,000 psi), Grade 8 is an inch-based standard with a tensile strength of 150,000 psi. In fact, Grade 8.8 bolts are more comparable in strength to Grade 5 bolts, not Grade 8.

Conclusion

In conclusion, knowing the different grades of bolts and their specific properties is crucial for any procurement officer or distributor in the industry. At Hengrui, we pride ourselves on offering top-quality, customizable fasteners to meet diverse industry needs. If you have any questions or need further information, feel free to contact us or visit our website.
Share The Post Now:
Recent Posts
Monica Song

Monica Song

Fastener Specialists

Hey, I’m the author of this post,
In the past 15 years, we have build long term cooperation relationship with many customers from North America, Europe, South America, Asia, Africa.
If you have any problems with it,
call us for a free, no-obligation quote
or discuss your solution.

You may also find these topics interesting

threaded rods

How are B7,B16 threaded rods manufactured?

Threaded rods are deceptively simple components, yet they are essential to structural engineering and industrial applications. Today, I’ll guide you through the production process of B7 and B16 threaded rods—from

Read More »

Ask For Quote Now!

Seraphinite AcceleratorOptimized by Seraphinite Accelerator
Turns on site high speed to be attractive for people and search engines.