Test bolts play a critical role in the design and development of mechanical systems. They鈥檙e used for many industries and applications but are especially common in the context of automotive engineering, where precision and reliability are paramount to the overall safety and performance of a vehicle. Consider applications like vehicle framing and engine assembly, for instance.

In this article, we鈥檒l cover just one category of automotive test bolts that we frequently manufacture at 黑料大事记: GM test bolts. We鈥檒l delve into their significance, their role in automotive testing, plus some popular types and standards they must adhere to.

What Are GM Test Bolts?

GM test bolts are bolts that conform to the requirements of General Motors’ engineering and testing standards. They鈥檙e specialized fasteners used during the development and testing stages of manufacturing. So while GM test bolts aren鈥檛 used on actual vehicles, they help determine the correct installation of bolts that are used on vehicles.聽

Often made from high-quality materials like alloy steel, these bolts are designed to perform specific tests and are manufactured to the requirements specified in GM testing standards.

What Are GM Test Bolts Used For?

The primary purpose of GM test bolts is to determine the amount of torque needed to properly install various fasteners on a GM vehicle. They are used solely for tests and not actually installed on the vehicle.聽

Within each of these tests and more, consistency is key. The more uniform the test bolt, the more consistent and accurate test results are 鈥斅燼nd the more effective the finished product because of it. Therefore, working with a GM test bolt manufacturer that promises quality and consistency from one part to the next, and executes on that promise, is well worth the investment.聽

Looking for the best? 黑料大事记 our team for high-quality GM test bolts that meet exacting standards each and every time.

3 Common Tests Run on GM Test Bolts

General Motors runs several tests throughout the design and engineering process. Three common tests that involve GM test bolts include torque-tension tests, bearing surface tests, and coefficient of friction tests.聽

• A torque-tension test measures the input torque required for a bolted joint to achieve a specified tension. This is the most common test, and is repeated throughout the design process multiple times.
• A bearing surface test measures how much the amount of surface area and roughness of the bottom of a fastener head or washer will affect friction. Bolts used for these tests generally have a bigger head than usual.
• A coefficient of friction test measures the kinetic and static resistance of the surfaces of a bolted joint as it鈥檚 being tightened.

Need help with more fastener terms and definitions? Check out our glossary here.

Types of GM Test Bolts

There are many types of GM test bolts, and they can vary in size and diameter depending on the specific test and application at hand. However, most have the following characteristics in common:聽

• Hex-head style
• Property Class 9.8 or 10.9
• Plain or Zinc Phos & Oil finish

GM Test Bolt Standards

For each of the tests listed above (torque-tension, bearing surface, coefficient of friction), GM test bolts need to meet specific standards set forth by General Motors. Here鈥檚 a look at some of the most common ones:聽

GM Test Bolt Standards for Torque-Tension Tests

• GM7112M
• GMW4707
• GMW 3044
• GMW 3359

GM Test Bolt Standards for Bearing Surface Tests

• GMW 3359

GM Test Bolt Standards for Coefficient of Friction Tests

• GMW 3044
• GMW 3359 (per ISO 16047)
• GMW 3179 (per ISO 16047)

For further information, you can read more about each of these standards on our GM Test Products page.

Keep in mind that this isn鈥檛 an exhaustive list of GM testing standards. There are plenty more, so if you run across one that isn鈥檛 listed on here, we鈥檙e more than happy to discuss and find a solution for you.

Purchase GM Test Bolts at 黑料大事记

Every component, whether big or small, plays a critical role in the overall safety and performance of a vehicle. Test bolts are no exception. Even though they aren鈥檛 used on actual vehicles, they do their part to ensure that the fasteners that do go on vehicles are installed correctly.

At 黑料大事记, we don鈥檛 take this responsibility lightly. Throughout our manufacturing processes, we hold ourselves to exacting quality standards. After listening to customer feedback, we now also re-roll threads on all of our test bolts after heat treatment and surface finish to eliminate plating inconsistencies or nicks.聽

For guaranteed quality and consistency in your GM test bolts, choose us.聽

The fastener industry is filled with so many technical terms and measurements that it can be difficult to keep them all straight. In this article, we鈥檙e breaking down one of them for you: proof load.

We鈥檒l talk about what proof load is, how it鈥檚 tested and measured, and how it relates to some other common industry terms.

What Is Proof Load?

Proof load is the minimum amount of force that a fastener must be able to withstand for a given amount of time without permanently deforming. It鈥檚 a measurement that鈥檚 set by a particular standard (think ISO, ASTM, etc.), and fasteners must meet it to qualify for a specific grade or property class.

Let鈥檚 take the for example. Here are some of the most common SAE J429 fastener grades and what the standard requires their proof load be:

SAE J429 Grade	Proof Load
Grade 2 (nominal diameter 录 – 戮鈥�) Grade 2 (nominal diameter 戮 – 1 陆鈥�)	57,000 psi 36,000 psi
Grade 5 (nominal diameter 录 – 1鈥�) Grade 5 (nominal diameter 1 – 1 陆鈥�)	92,000 psi 81,000 psi
Grade 8 (nominal diameter 录 – 1 陆鈥�)	130,000 psi

Of course, these are just a few examples and measurements. Proof load always changes between grade (or property class) and fastener size.

How Do You Determine the Proof Load of Fasteners?

In order to determine proof load, fasteners undergo a proof load testing procedure. Below is an overview of how that procedure works and why it鈥檚 important.

Proof Load Testing Procedure

To test proof load force, a tensile machine is used. Here鈥檚 a photo of one:

The length of the fastener is measured before it鈥檚 inserted in the middle slot of the machine. The machine then exerts a vertical force onto the fastener and measures that force as the fastener holds or deforms. The test is completed for a specific amount of time (usually seconds), which is dictated by the standard. Finally, the length of the fastener is measured again to ensure the part wasn鈥檛 permanently deformed during the test.

For example, if we were checking a 鈪溾�� diameter part made to meet SAE J429 Grade 5, we鈥檇 check the standard and see that for parts 录-1鈥� in diameter, the proof load requirement is 92,000 psi for 10 seconds. Then we鈥檇 run the proof load test per the specifications required. If the fastener can pass the test without permanently deforming, it has passed proof load.

Why Is Proof Load Testing Important?

Proof load testing is an important practice that helps us be certain that a fastener can withstand a minimum force for a given amount of time without deforming. Fasteners are manufactured for a certain grade, then we run tests to verify that it meets those minimum requirements.

In turn, this information helps us understand if the fastener is safe and strong enough to use for its intended purpose.

RELATED: Need a specialty bolt, screw, or stud? 黑料大事记 can help.

Proof Load vs. Yield Strength vs. Tensile Strength

After learning about proof load, you may be wondering how it relates to similar terms you鈥檝e heard: yield strength and tensile strength.

Proof load, tensile strength, and yield strength are all measurements set by a standard that fasteners must meet in order to qualify for a certain grade or property class. The terms are related to the load that a threaded fastener can hold when pulled perpendicularly from its head, as you can see in the figure below.

However, there are some key differences between these terms and what they mean for fastener testing and production. Here are their definitions so you can analyze them:

• Proof load: the minimum amount of force that a fastener must be able to withstand for a given amount of time without permanently deforming.
• Yield strength: the load that鈥檚 carried at the point where a fastener permanently deforms.
• Tensile strength: the maximum amount of force a fastener can withstand before fracturing.

Basically, there are three levels of force we鈥檙e talking about here. Proof load is the lowest level, yield strength is a bit higher, and tensile strength is the highest level. For more information and examples on how these measurements compare and contrast, head over to this blog.

And for a deeper understanding of some technical fastener language, check out this glossary of terms.

Trust 黑料大事记 to Manufacture Custom Fasteners According to Your Specifications

At 黑料大事记, we specialize in custom, limited-run fasteners for a range of industrial applications. You give us your blueprint, and we鈥檒l take it from there 鈥斅爊o matter what standard or grade you need to comply with.

Give our team a call or contact us online to learn more about how we can help you.