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Hex Bolts vs Hex Cap Screws: Understanding the Key Differences

04 Aug.,2025

Hex Bolts vs Hex Cap Screws: Understanding the Key Differences

Bolts and cap screws are both essential fasteners that are used in a wide range of applications. While they may seem similar, they have some significant differences that can affect their performance and suitability for different tasks. In this blog, we will explore the key differences between bolts and cap screws to help you choose the right fastener for your needs.

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Key Features of bolts and cap screws

The two major features of bolts and cap screws: bearing surface and chamfered end.

Bolts and cap screws differ in their design and features. One of the key differences is the presence of a bearing surface and chamfered end on the cap screw. The bearing surface, also known as the washer face, helps prevent damage to the mating surface during assembly. This is especially critical for assemblies using thin or soft materials. The chamfered end, also known as a point, reduces the potential for cross-threading with mating products. These features facilitate assembly and could help reduce the time and cost involved. It's important to note that only the hex cap screw has these features, making it an ideal choice for certain applications.

Attributes of Bolts and Cap Screws

Under-Head Radii and Body Diameter

The under-head radii and body (or “shank”) diameters. The hex bolt; has a higher maximum tolerance on its under-head radius and body diameter than the cap screw which potentially makes its under-head juncture much sturdier and resistant to fracturing and failures. However, the lower side of its tolerances are below that of a typical cap screw. Which could provide varying results in performance.

Though similar, only the hex cap screw can be interchanged with most comparable assemblies using a hex bolt. Unfortunately, the same cannot be said for the hex bolt, as its larger tolerance zones could easily compromise the integrity of assemblies that primarily utilize hex cap screws.

Understanding When Bolts and Cap Screws Can Be Used Interchangeably

Choosing the Right Fastener

When selecting a fastener, it is important to consider several factors, including the application, the materials being fastened, and the environmental conditions. It is important to choose the right fastener to ensure a secure and reliable connection.

Material Considerations for Fasteners

The application in which the fastener will be used is another important consideration. For example, if the fastener will be used in a high-stress application, a cap screw may be preferred over a bolt. Similarly, if the fastener will be used in an application where it will be subject to vibration, to prevent the fastener from loosening, a hex bolt combined with a lock washer may be preferred over a hex cap screw with a thread-locking compound.

Application Considerations for Fasteners

The application in which the fastener will be used is another important consideration when choosing the right fastener. For example, if the fastener will be used in a high-stress application, a cap screw may be preferred over a bolt. Similarly, if the fastener will be used in an application where it will be subject to vibration, a lock washer or thread-locking compound may be needed to prevent the fastener from loosening.

Conclusion

In conclusion, it's important to understand the key differences between bolts and cap screws, which primarily come down to their features and attributes. Hex cap screws have a bearing surface and chamfered end, while bolts do not. On the other hand, bolts have a higher maximum tolerance on their under-head radii and body diameter, which potentially makes their under-head juncture much sturdier than cap screws. However, cap screws are more interchangeable with other assemblies. When choosing the right fastener for your needs, it's important to consider the application and materials being used. By following these guidelines and understanding the differences between bolts and cap screws, you can make informed decisions and ensure the integrity of your assemblies.

Hex Head vs. Socket Head Bolts - FASTO

In the fastener industry, hex head bolts are widely used due to their superior performance over slotted or cross-recessed heads in terms of preventing stripped screws and offering higher torque. Hex head bolts can be divided into socket head (internal hex) bolts and external hex head bolts. Both types of bolts share similarities but also possess distinct differences that influence their application choices. This article explores these differences from several perspectives: structure, cost, tightening tools, advantages and disadvantages, and applications.

Ⅰ. Structure

Structurally, it is straightforward to distinguish between internal and external hex head bolts. The threaded sections are generally similar, while the main difference lies in the head design. External hex head bolts feature a six-sided head without an indentation. For increased bearing area, there's also the external hex flange bolt, which is widely used.

On the other hand, socket head bolts have a round exterior with a recessed hexagonal hole inside. Common variations include cylindrical, pan, countersunk, and flat head socket screws. There are also special types like set screws or machine screws that do not have a protruding head. To enhance the contact area, internal hex flange bolts are also available. Additionally, for controlling friction coefficients or enhancing anti-loosening properties, both external and internal hex combination bolts exist.

Contact us to discuss your requirements of Internal Hex Screw. Our experienced sales team can help you identify the options that best suit your needs.

Ⅱ. Cost

The threading process for both internal and external hex bolts is typically achieved through roll-threading using nearly identical dies, so the cost difference here is negligible. However, the manufacturing cost of the head varies significantly due to different mold requirements and production techniques. Internal hex bolts tend to have a higher head manufacturing cost compared to external hex bolts, which can be produced at approximately half the cost.

Ⅲ. Tightening Tools

In everyday use, internal hex bolts are tightened with "L"-shaped Allen wrenches, providing leverage for better force application. External hex bolts can be tightened with adjustable wrenches, box-end wrenches, or open-end wrenches. In production settings, quality assurance and automation requirements dictate the use of calibrated torque wrenches and precision tightening guns, requiring corresponding sockets: internal hex bolts need an external hex socket, while external hex bolts require an internal hex socket. Sockets come in various sizes to match the specific bolt head dimensions.

Ⅳ. Advantages and Disadvantages

Advantages

External Hex Bolts/Screws: Provide good self-locking; larger pre-tightened contact area and force; wider full-thread length options; can fix part positions with clearance holes and withstand shear forces.
Internal Hex Bolts/Screws: Easy to tighten; less likely to strip; occupy minimal space; can be flush-mounted for a neat appearance without interfering with other components.

Disadvantages

External Hex Bolts/Screws: Take up more space and are unsuitable for delicate areas; cannot be used as countersunk bolts.
Internal Hex Bolts/Screws: Smaller contact area and lower pre-tightened force; limited full-thread length for longer bolts; harder to equip tightening tools, prone to stripping, and difficult to replace or remove.

Ⅴ. Applications

Choosing between internal and external hex bolts depends on the specific application requirements. If a large axial force and ample tightening space are required, external hex bolts are preferred. For locations with spatial constraints or aesthetic considerations, such as needing a countersunk finish and minimal visible impact, along with smaller axial forces and torques, internal hex bolts are ideal.

Automotive examples illustrate this selection process: for connecting subframes to the body, where visibility isn't a concern and significant axial force and torque are needed, external hex bolts are suitable. Conversely, interior component connections, which must meet visual standards and may require flush mounting, benefit from internal hex bolts or screws due to their compactness and aesthetics.

To summarize, if your application demands precision, beauty, or has assembly space limitations, opt for internal hex bolts/screws. Otherwise, choose external hex bolts/screws for their cost-effectiveness and adequate performance. This is why external hex bolts/screws find broader applications in various industries.

Are you using hex head or socket head bolts in your projects? And if you have any questions about how to choose the right hex head bolts/screws for your needs, don't hesitate to reach out.

For more information, please visit Lead Screw and Screw Nut.

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