Bolts are available in a wide variety of different grades, which usually indicate a bolt's tensile strength. Typically, bolts are steel fasteners that are engineered with external male threads. Marsh Fasteners explains the tensile strength and grades of bolts for various applications. Read on to find out more.
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So, what is the tensile strength of a bolt? In simple terms, the tensile strength is the maximum amount of stress or pressure a bolt can withstand. Therefore, the higher the tensile strength, the greater the impact the bolt can bear, making it suitable for high-stress applications such as industrial machinery or securing heavy objects to each other. The most common high tensile bolts are:
Grade 8.8 bolts: Also known as structural grade bolts, they are typically made of steel and plated with several coatings.
Grade 10.9 bolts: As these bolts are most often used in the automotive industry, they are also referred to as 'car bolts'. They are made of boron or carbon steel and have high tensile strength ( MPa).
Grade 12.9 bolts: Known for their strength, these bolts are most often used in the manufacturing and construction industries to join medium or heavy industrial parts such as an automotive engine.
Grade 14.9 bolts: It's simple: these are the most durable bolts you can use in your application. Perfect to join large structural elements to each other, the grade 14.9 bolt has a whopping maximum tensile strength of MPa.
Now that you know how tensile strength is useful in choosing the right bolt for your application, Marsh Fasteners explains the various grades of bolts and the applications they are used for. Here is a general breakdown:
These grades start at grade 2 and go up to grade 8, which is the strongest SAE American Grade bolt available.
Grade 2
A grade 2 bolt is distinguished through its complete lack of markings and will usually have a tensile strength of between 60,000 and 74,000 psi. Depending on the application they are used for, the Grade 2 bolts can be partially or completely threaded. These bolts are generally used for non-critical joints and applications in design, OEM and maintenance, especially as it is a cost-effective option. The nominal size range of the grade 2 bolt is ¼ inch to 4 inches.
Manufactured from medium carbon steel and hardened for greater strength and durability, a grade 5 bolt is distinguished by 3 radial lines and promises tensile strengths between 105,000 and 120,000 psi. They are most commonly found in automotive applications or those that require medium strength. The most common sizes of Grade 5 bolts range from ¼ inch to 1½ inches.
The high-strength, sought-after grade 8 bolt can be distinguished by six raised dashes. Its medium-carbon alloy steel has been quenched and tempered, ultimately making it possible to achieve an impressive tensile strength of 150,000 psi, compared to a grade 2 bolt's 64,000 psi. In other words, a grade 8 bolt is more than twice as strong as a grade 2 SAE American Grade bolt. You will often find grade 8 bolts in demanding applications, such as in automotive suspensions. Other applications that require the strength and tolerance of a grade 8 bolt are industrial machinery, motors, pumps, valves and tanks!
The heavy-duty grade S bolts are built for strength and durability. They are engineered to withstand stresses ranging from 45 to 49.9 MT per 6.45 cm3.
Ultimately, the bolt that you select will depend on how strong it needs to be. The more demanding the application, the higher the grade that will be required.
When it comes to SAE American Graded bolts, you can always turn to Marsh Fasteners for the finest selection and quality. Contact us now for more information.
We've discussed bolt grades in some of our past articles. However, like many topics in the fastener industry, they can be a bit tricky to fully understand. We explain what bolts grades are, how they're categorized, and what some of their uses are below. That way, you'll hopefully gain a better idea of what bolt grade you need for your application.
Bolt grades are defined by their specific material, as well as the strength of that material. This helps to determine the maximum amount of stress that the bolt can handle. Typically, a bolt grade spec will call out the material (or give a couple of material options), then list the strength requirements for that material.
If you're working with carbon or alloy steel bolts (which are the most common), these strength requirements are determined by the hardness requirements for that material. The harder the material, the higher the bolt strength. Many specs may also have proof load or tensile strength requirements, but these are really just a confirmation of the strength that's called out in the hardness requirements.
Overall, bolt grades are useful to be aware of when you're deciding which kind of bolt you need for your particular application.
SAE, ISO, and ASTM are three of the main governing bodies that create standards to set the rules for bolt grading systems. While there are many other governing bodies, each with their own long list of grading standards, we're sticking to these three as examples in this article. They're of the most common we deal with here at Wilson-Garner, but that's not necessarily the case for every manufacturer.
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Each of these systems have their own standards and naming conventions, but they generally follow the same rule for bolt grades ' the higher the grade, the stronger the bolt. If you're unsure about the grade or material of a particular bolt, looking at its head is a good place to start, as most standards define head marking requirements for most grades.
SAE stands for the Society of Automotive Engineers. Its standards are one of the most common for inch parts. SAE J429 is the standard developed for bolt, screw, stud, sem, and U-bolt specifications.
For bolts, you can find the SAE J429 grade displayed in radial lines on the head, which indicate the grade and strength requirements.
More on SAE J429 grades, specifications, and head markings here.
ISO stands for the International Standards Organization. ISO 898-1 is the most commonly used standard for metric grades, or property classes (the technically correct terminology for metric bolt grades). It dictates the standard for bolts, screws, and studs made from carbon steel and alloy steel. It includes 10 different property classes.
For bolts, you can find the ISO 898-1 property class displayed in raised or depressed numbers on its head.
More on ISO property classes, specifications, and head markings here.
ASTM stands for the American Society for Testing and Materials. ASTM A307 is the standard developed for bolts and studs, and it creates two different grades: Grade A and Grade B. You'll find the grade listed as 307A or 307B on the bolt head.
More on ASTM A307 grades, specifications, and head markings here.
Now let's jump into some specific bolt grades and their applications. But first, let us say that there are many different bolt grades out there. For the sake of brevity, we'll just be discussing a few of the most common bolt grades within each of the systems listed above.
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We should also mention that each of the system and bolt grades listed above are for bolts made of carbon or alloy steel. However, there are also many bolt grades for other materials, like stainless steel or titanium.
For example, some stainless steel and titanium bolt grades include:
Stainless Steel
Titanium
While we don't work with these materials at Wilson-Garner, we're happy to try and answer any questions you have about them or direct you to a solution that might work better for your application.
Not sure which bolt grade is right for your application? Talk to the team at Wilson-Garner! Our specialty fastener experts can help you determine the best solution, then manufacture parts that fit your specifications in limited-run quantities. If you have any questions, feel free to reach out via call or our online contact form.
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