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The Different Grades of Bolts – Bolt Grades Explained & Bolt Grades Chart

Bolts are fundamental components in construction, manufacturing, and various industries where fastening and securing are crucial. They come in various shapes and sizes, but what truly distinguishes them are their grades. Bolt grades determine their strength, durability, and suitability for specific applications. In this comprehensive guide, we will delve into the world of bolt grades, explaining their significance, standards, and practical uses. To aid in your understanding, we will also provide a detailed bolt grades chart for reference.

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What is a Bolt?

Bolts are foundational mechanical fasteners used extensively in construction, manufacturing, automotive, and countless other industries. They are designed to hold components together by creating a clamping force through the application of torque. Bolts serve a vital role in ensuring the stability, safety, and reliability of various structures and machinery.

At its core, a bolt consists of three primary elements:


The head of a bolt is the topmost part and typically features a distinct shape, such as hexagonal (hex), round, square, or other designs. The choice of head shape depends on the application’s requirements and the tools or equipment used for tightening. The head allows for external manipulation, such as turning with a wrench or screwdriver, to drive the bolt into place or remove it when necessary.


The shank is the elongated, cylindrical body of the bolt that extends from the head to the tip. It is the part of the bolt that contains the threads. Threads are helical grooves or ridges spiraling around the shank’s exterior. These threads are essential for creating a secure connection by engaging with a corresponding threaded hole or nut.

3.Tip or Point

The tip or point of the bolt is the lower end of the shank that comes into contact with the components being fastened. The design of the tip can vary, with options like pointed tips for easy alignment, flat tips for distributing load forces, or rounded tips for specific applications. The tip’s design plays a role in how the bolt interacts with the materials it is securing.

The Anatomy of a Bolt

To gain a more comprehensive understanding of the inner workings of a bolt, let’s explore its anatomy in greater detail:

1.Threaded Portion

The threaded portion of the bolt is the segment of the shank containing the threads. Threads are meticulously cut or rolled onto the shank, forming a spiral pattern. These threads are the key to creating a secure joint. When the bolt is rotated into a threaded hole or engaged with a nut, the threads grip the complementary threads, allowing the bolt to be tightened and secured.

2.Unthreaded Portion

Above the threaded portion, there is often an unthreaded section of the shank. This unthreaded portion serves several crucial purposes. Firstly, it helps in aligning the bolt as it is inserted into a hole or through components, ensuring that the threads engage correctly. Secondly, it provides a smooth surface for the head to press against when clamping the components together.

3.Head Type

Bolt heads come in various shapes and designs, each tailored to specific applications and requirements. Common head types include hexagonal (hex) heads, which provide excellent torque transfer capabilities; round heads, which offer a clean and unobtrusive appearance; and square heads, which are less common but excel at transferring high levels of torque. The choice of head type depends on factors such as the required torque, access to the bolt, and aesthetic considerations.

4.Drive Type

The drive type of a bolt head refers to the type of tool or driver used to turn the bolt. Common drive types include hexagonal (hex) drives, Phillips drives, slotted drives, Torx drives, and Allen (hexagonal socket) drives, among others. The choice of drive type depends on the specific needs of the application, the level of torque control required, and the available tools for installation.


Bolts are manufactured from a wide range of materials to suit various applications and environmental conditions. Some common bolt materials include steel, stainless steel, aluminum, brass, and more. The material choice is critical as it determines factors like strength, corrosion resistance, and weight-bearing capacity.

Bolts are fundamental components that play a pivotal role in countless industries and applications. Their basic structure, consisting of a head, shank, and tip, allows them to securely fasten components together. The threads on the shank engage with complementary threads in nuts or holes, creating a strong, reliable connection. Understanding the anatomy of a bolt is essential for selecting the right bolt type for specific tasks and ensuring the integrity of assembled structures or machinery.

Chapter 1: Bolt Grades

Bolt grades are a fundamental aspect of understanding the suitability and performance of bolts in various applications. In this chapter, we will delve into the world of bolt grades, exploring their significance, standards, and classifications. By the end of this chapter, you will have a comprehensive understanding of how bolt grades play a crucial role in determining the strength and reliability of fasteners.

1.Significance of Bolt Grades

Introduction to Bolt Grades

Bolt grades are a system of classification that indicates the material and strength properties of a bolt. Understanding these grades is essential because they determine the bolt’s ability to withstand different loads, pressures, and environmental conditions. The right bolt grade ensures the safety and integrity of various structures and equipment.

Why Do Bolt Grades Matter?

The importance of choosing the correct bolt grade cannot be overstated. Bolt failure can lead to catastrophic consequences in industries such as construction, automotive, aerospace, and manufacturing. We will explore real-world examples where selecting the wrong bolt grade has resulted in costly failures and safety hazards.

2.Bolt Grade Standards

Overview of Standards

To maintain consistency and reliability, bolt grades are standardized globally. Various standards organizations, such as the Society of Automotive Engineers (SAE), ASTM International, and the International Organization for Standardization (ISO), establish guidelines for bolt grades. We will examine the role of these organizations and the standards they set.

SAE J429 Bolt Grades

The SAE J429 standard is widely used in North America to classify and specify bolt grades. We will provide an in-depth look at the SAE J429 bolt grades, including Grade 2, Grade 5, and Grade 8, and discuss their properties and applications.

ASTM A307 Bolt Grades

ASTM A307 is another important standard that classifies bolts based on their material and strength properties. We will explore the ASTM A307 bolt grades and their suitability for specific applications.

ISO Bolt Grades

For international applications, ISO standards play a significant role in classifying bolts. We will discuss ISO standards and how they relate to bolt grades, ensuring compatibility and uniformity across borders.

3.How are Bolt Grades Classified?

The Classification Methods

Bolt grades are typically indicated by markings on the bolt head or packaging. These markings can take the form of numbers, lines, dots, or other identifiers. We will explore the various classification methods used to distinguish different bolt grades and what these markings signify.

Reading Bolt Grade Markings

Understanding how to read bolt grade markings is essential for selecting the right fasteners. We will provide practical guidance on deciphering these markings, ensuring that you can identify bolt grades accurately and confidently.

In this chapter, we have laid the groundwork for understanding bolt grades. You now have a solid foundation in recognizing the significance of bolt grades, the organizations that establish standards, and the classification methods used to differentiate between different grades. As we move forward in this guide, we will dive deeper into specific bolt grades, their properties, and practical applications, allowing you to make informed decisions when choosing fasteners for your projects.

Chapter 2: Understanding Bolt Materials

Bolts come in various materials, each with its unique properties and suitability for specific applications. In this chapter, we will explore the world of bolt materials, ranging from common steel bolts to non-ferrous options like aluminum and brass. Understanding these materials is crucial for selecting the right bolt for your project, taking into account factors such as strength, corrosion resistance, and environmental conditions.

1.Steel Bolts

Steel is the most widely used material for bolts due to its exceptional strength and versatility. We will discuss the reasons behind the popularity of steel bolts and their various advantages.

Types of Steel Bolts

Steel bolts come in different types, including carbon steel, alloy steel, and stainless steel. We will explore these variations, highlighting their specific properties and applications.

  • Carbon Steel Bolts:Carbon steel bolts are known for their strength and affordability.
  • Alloy Steel Bolts:Alloy steel bolts are engineered for even higher strength and durability.
  • Stainless Steel BoltsStainless steel bolts are prized for their corrosion resistance.

2.Non-ferrous Bolts

Non-ferrous bolts, made from materials other than iron or steel, have unique advantages, such as corrosion resistance and lightweight properties. We will discuss the reasons for choosing non-ferrous bolts and their role in specific industries.

  • Aluminum Bolts:Aluminum bolts are lightweight and corrosion-resistant, making them ideal for applications where weight reduction and weather resistance are crucial.
  • Brass Bolts:Brass bolts offer excellent corrosion resistance and an attractive appearance. They find applications in both functional and decorative settings.
  • Bronze Bolts:Bronze bolts, known for their strength and durability, are often used in marine and architectural applications.
  • Other Non-ferrous Bolts:In addition to aluminum, brass, and bronze, there are other non-ferrous materials used to manufacture bolts, such as copper and titanium.

3.Material Selection Considerations

Factors Affecting Material Choice

Choosing the right bolt material is a critical decision that depends on various factors, including the application’s load requirements, environmental conditions, and budget constraints. We will provide guidance on how to make informed material selection decisions.

Compatibility with Other Materials

Bolt materials must be compatible with the materials they are fastening. We will discuss the importance of material compatibility and provide recommendations for ensuring a reliable and long-lasting connection.

In this chapter, we have delved into the world of bolt materials, including the various types of steel bolts and non-ferrous options like aluminum, brass, and bronze. Understanding the properties and characteristics of these materials is essential for selecting the right bolts for your projects, whether they involve heavy structural applications, marine environments, or decorative installations. As we continue our exploration of bolts, we will build upon this knowledge to guide you in making informed choices for your specific needs.

Chapter 3: The Different Grades of Bolts

Bolt grades are a critical factor in determining a fastener’s strength, durability, and suitability for various applications. In this chapter, we will delve into the details of different bolt grades, their properties, and practical applications. By the end of this chapter, you will have a comprehensive understanding of various bolt grades, helping you choose the right fasteners for your specific needs.

Bolt Grades Chart Overview

A bolt grades chart is a practical reference guide that summarizes the properties and applications of different bolt grades. We will introduce the bolt grades chart as a valuable tool for quick and easy reference when selecting fasteners.

We will outline the structure of the bolt grades chart, which typically includes columns for grade numbers, properties (such as tensile strength and yield strength), and common applications. Understanding how to navigate the chart is essential for choosing the right bolt grade.

Grade 2 Bolts

Grade 2 bolts are among the lowest grade of standard bolts. We will explain their properties, which make them suitable for specific applications that do not require high tensile strength.

Grade 2 bolts find use in non-critical applications where their moderate strength and cost-effectiveness are sufficient. We will provide examples of situations where Grade 2 bolts are appropriate.

Grade 5 Bolts

Grade 5 bolts are known for their improved strength compared to Grade 2. We will discuss their properties, such as higher tensile strength and where they fit within the hierarchy of bolt grades.

Grade 5 bolts are widely used in automotive, machinery, and construction applications. We will explore these common uses and discuss why Grade 5 bolts are a popular choice.

Grade 8 Bolts

Grade 8 bolts represent a significant step up in terms of tensile strength and durability. We will delve into the characteristics that make Grade 8 bolts suitable for demanding applications.

Grade 8 bolts are often employed in critical applications where safety and load-bearing capacity are paramount. We will provide examples of industries and situations that rely on Grade 8 bolts.

Bolt Grade Selection Guide

Selecting the appropriate bolt grade is crucial for the success and safety of any project. We will provide a step-by-step guide to help you make informed decisions based on load requirements, environmental conditions, and other factors.

In this chapter, we have explored various bolt grades, their properties, and practical applications. Understanding the strengths and limitations of different bolt grades is essential for selecting fasteners that meet the specific demands of your projects. As we continue in this guide, we will build upon this knowledge to guide you in choosing the right bolt grades for your unique applications.

Chapter 4: The Different Grades Of Bolts? Here Are Commonly Used Bolt Grades

Bolt grades in the range of 4.6 to 12.9 are commonly used in the market, particularly in regions that follow metric bolt standards. These grades represent different levels of tensile strength, and their selection depends on the specific requirements of various applications. Here is an overview of these commonly used metric bolt grades:

  • 4.6 Grade Bolts: Bolts in this grade typically have a tensile strength of around 400 MPa. They are used in applications where moderate strength is sufficient, such as general construction, machinery, and automotive components.
  • 5.6 Grade Bolts: While less common than some other grades, 5.6 grade bolts have a tensile strength of approximately 500 MPa. They may be used in applications where slightly higher strength is needed, but still not in highly critical or heavy-duty situations.
  • 8.8 Grade Bolts: Bolts with an 8.8 grade have a significantly higher tensile strength of around 800 MPa. They are commonly used in structural applications, including building and bridge construction, as well as in machinery and equipment.
  • 10.9 Grade Bolts: These bolts offer even greater tensile strength, typically around 1000 MPa. They are used in critical applications where high strength and reliability are essential, such as automotive chassis components and heavy machinery.
  • 12.9 Grade Bolts: 12.9 grade bolts are the highest strength bolts among the commonly used metric grades, with a tensile strength of approximately 1200 MPa. They are used in extremely demanding applications, including aerospace, high-performance automotive components, and specialized machinery.

These grades adhere to ISO metric bolt standards, and their numerical values indicate the minimum tensile strength in megapascals (MPa). Proper selection of the bolt grade is crucial to ensure that fasteners meet the load and safety requirements of specific projects. Engineers and designers carefully consider these factors when choosing the appropriate bolt grade for their applications.

Chapter 5: Bolt Grades Chart – Metric Bolt Grades & Strength Chart

A Bolt Grades Chart is a valuable reference tool that provides information about different metric bolt grades and their corresponding strength characteristics. Below is a Metric Bolt Grades & Strength Chart that outlines commonly used metric bolt grades and their tensile strengths:

Bolt GradeTensile Strength (MPa)

When selecting bolts for a project, it’s crucial to consult engineering standards and guidelines to ensure that the chosen bolt grade meets the required safety and load-bearing criteria. Additionally, consider factors like the environment in which the bolts will be used, as corrosion resistance may also be a critical consideration.

Chapter 6: Summarize

In the final chapter, we will summarize the key takeaways from this extensive guide on bolt grades. We will emphasize the importance of choosing the right grade for specific applications and the role of standards in ensuring reliability.

Our exploration of bolts has been both educational and practical. Whether you’re a professional engineer or a DIY enthusiast, understanding the intricacies of bolts is essential for project success and safety. The right bolt, properly selected and installed, ensures the integrity of structures, machinery, and countless other applications.

As you embark on your future projects, remember the importance of matching the bolt grade and material to the specific demands of the task. Consult standards, seek expert advice when needed, and always prioritize safety.

Thank you for joining us on this journey through the world of bolts. We hope this guide has been a valuable resource in expanding your knowledge and enhancing your ability to make informed decisions when it comes to selecting and using bolts.