1. Introduction to Blind Rivet Nuts

What is a Blind Rivet Nut? 

A blind rivet nut, also known as a rivet nut or nutsert, is a type of threaded insert designed to be installed in a workpiece from one side (blind side). It’s a tubular fastener with internal threads. When installed, it forms a secure, permanent, load-bearing thread in thin materials like sheet metal, plastics, or composite materials where tapping a thread is impractical or impossible.

Why Use Blind Rivet Nuts?

Blind rivet nuts offer a practical solution for creating a strong anchor point in thin materials. They provide a sturdy, reusable thread for subsequent fastening with a bolt or screw.

Here’s why they’re so useful:

• One-Sided Access: They can be installed when access to the backside of the material is limited or nonexistent.
• Strong Threads: They create robust, reliable threads in materials too thin to be tapped.
• No Material Deformation: They don’t deform the base material during installation, unlike traditional welding, which can cause warping.
• Versatility: They can be used to join different materials or to attach components to a single material.
• Aesthetics: They provide a clean, finished appearance with no protrusions on the back side.

Brief History and Evolution

The concept of a blind rivet nut dates back to the 1930s, originally developed by the BFGoodrich company for de-icing aircraft wings. The first versions were a type of rubber rivet nut called Rivnuts, which would expand and create a secure attachment. Over time, the technology evolved from rubber to metal and the tools became more sophisticated, leading to a wider range of applications across various industries.

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2. Types of Blind Rivet Nuts

Blind rivet nuts come in a variety of styles, categorized mainly by their body shape, head style, and material.

By Body Shape

• Round Body Rivet Nuts: The most common and simple type. They require a round hole and are best for applications where there’s no rotational stress.
• Hex Body Rivet Nuts: Designed to fit into a pre-punched hex-shaped hole. This shape provides excellent resistance against spinning or rotation.
• Splined Body Rivet Nuts: Feature a series of splines (grooves) along the body that bite into the host material, providing enhanced spin-out resistance.

By Head Style

• Flat Head Rivet Nuts: Also known as a “flange” or “large flange” head, this style provides the largest bearing surface against the material, offering strong pull-out resistance.
• Countersunk Head Rivet Nuts: Used for a flush, low-profile finish. The head sits level with the surface of the material, which is ideal for cosmetic applications.
• Low Profile Head Rivet Nuts: A smaller version of the flat head, offering a more discreet appearance while still providing a good bearing surface.

By Material

• Steel Rivet Nuts: The most common and cost-effective option. They offer good strength and are often zinc-plated for corrosion resistance.
• Stainless Steel Rivet Nuts: Used for superior corrosion resistance and high-temperature applications. They are stronger and more durable than aluminum but less common than steel.
• Aluminum Rivet Nuts: Lightweight and corrosion-resistant. They are softer than steel or stainless steel and are ideal for use in aluminum parts to prevent galvanic corrosion.

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3. Blind Rivet Nut Sizes and Dimensions

Understanding Thread Size (Metric and Imperial)

When selecting a blind rivet nut, the thread size is the most crucial dimension. This is the internal thread that a bolt or screw will fasten into. Sizes are standardized in both metric and imperial systems.

• Metric Sizes: These are designated by an “M” followed by the thread diameter in millimeters (mm). Common sizes include M3, M4, M5, M6, M8, M10, and M12.
• Imperial Sizes: These are designated by a number (for sizes smaller than 1/4 inch) or a fraction (for 1/4 inch and larger), followed by the threads per inch (TPI). Common sizes include #6-32, #8-32, #10-24, 1/4-20, and 5/16-18.

Grip Range: How to Select the Correct Size

The grip range is the total thickness of the material(s) that the rivet nut is designed to fasten. Selecting the correct grip range is critical for a secure installation. If the material is too thin for the rivet nut’s grip range, the fastener will not fully collapse and secure properly. If the material is too thick, the rivet nut may not collapse at all, or it could be improperly installed, potentially leading to a weak joint. Manufacturers provide a specific grip range for each rivet nut, and it’s essential to match this range to the thickness of your workpiece.

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4. Materials and Finishes

Blind rivet nuts are available in a variety of materials and finishes, each chosen for specific applications based on strength, weight, and corrosion resistance requirements.

Steel

Steel rivet nuts are the most common and economical choice. They offer excellent strength and are suitable for a wide range of general-purpose applications. They’re often zinc-plated to provide corrosion resistance, with finishes like clear, yellow, or black zinc.

Stainless Steel

For applications requiring superior corrosion resistance, such as those in marine or chemical environments, stainless steel rivet nuts are the ideal solution. They are typically made from different grades of stainless steel, with 304 and 316 being the most common. 304 stainless steel offers good corrosion resistance for general use, while 316 provides even better resistance, particularly against chlorides and other corrosive agents. Stainless steel rivet nuts are stronger than aluminum but more expensive than steel.

Aluminum

Aluminum rivet nuts are valued for their lightweight properties and natural resistance to corrosion. They are a good choice for automotive, aerospace, and electronics applications where weight is a critical factor. Because aluminum is softer than steel, these rivet nuts require less force to install, making them easier to use with hand tools. They are also ideal for fastening to aluminum materials to prevent galvanic corrosion.

Protective Coatings and Finishes

In addition to the base material, rivet nuts can have various coatings to enhance their performance and appearance:

• Zinc Plating: A very common and cost-effective finish that provides a sacrificial layer to protect the steel from rust.
• Black Oxide: Provides a black, non-reflective finish for cosmetic purposes and offers some minor corrosion resistance.
• Galvanized: A thicker zinc coating applied for high-level corrosion protection, suitable for outdoor or harsh environments.
• Nickel Plating: Provides a bright, decorative finish and good corrosion resistance.

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5. Applications of Blind Rivet Nuts

Blind rivet nuts have become a staple in many industries due to their versatility and ease of use. Their ability to provide a strong, reusable thread in thin materials makes them invaluable for a wide array of fastening tasks.

Automotive Industry

In the automotive sector, blind rivet nuts are used for a variety of purposes, including:

• Interior Components: Fastening trim, dashboards, and other interior panels where a secure, hidden thread is needed.
• Body Panels: Attaching body panels and fenders without deforming the sheet metal.
• Aftermarket Accessories: Providing mounting points for accessories like roof racks, spoilers, and brackets.

Aerospace Industry

In aerospace, the need for lightweight, strong, and reliable fasteners is paramount. Blind rivet nuts are used for:

• Aircraft Structures: Attaching non-structural components like brackets and fixtures.
• Interior Fixtures: Securing seats, galleys, and overhead bins.
• Access Panels: Creating reusable fastening points for maintenance and inspection panels.

Construction

Blind rivet nuts are used in construction for both structural and non-structural applications, such as:

• Railing Systems: Attaching handrails to metal structures.
• Facades: Mounting exterior panels to building frames.
• HVAC Systems: Assembling ductwork and mounting equipment.

Electronics

In the electronics industry, blind rivet nuts are used to:

• Equipment Mounting: Providing secure anchor points for components inside computer chassis, servers, and control panels.
• Enclosure Assembly: Assembling the cases and enclosures of electronic devices.

General Manufacturing

Blind rivet nuts are widely used in general manufacturing for:

• Appliances: Fastening components in refrigerators, washing machines, and other household appliances.
• Machinery: Attaching covers, guards, and access panels to machinery and equipment.
• Furniture: Assembling metal furniture and providing strong joints in tubular structures.

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6. How to Install Blind Rivet Nuts

Installing a blind rivet nut is a straightforward process that can be done with the right tools. The basic principle involves deforming the body of the rivet nut to create a secure bulge on the blind side of the material.

Tools Required

• Hand Riveters: Manual tools for low-volume, occasional use. They are affordable and easy to operate but require more physical effort.
• Pneumatic Riveters: Air-powered tools for high-volume and production line applications. They are fast and reduce operator fatigue.
• Electric Rivet Tools: Cordless, battery-powered tools that offer portability and convenience, ideal for on-site work where air lines are not available.
• Spin-Pull Tools: Specialized tools that use a combination of spinning and pulling to install the rivet nut, providing a very precise and consistent result.

Step-by-Step Installation Guide

1. Preparing the Hole: Drill or punch a hole in the workpiece that matches the specified diameter for the rivet nut. The hole size is critical for a secure installation. An oversized hole can lead to spinning, while an undersized one can prevent proper insertion.
2. Inserting the Rivet Nut: Place the rivet nut onto the mandrel of the installation tool. Insert the rivet nut into the prepared hole.
3. Setting the Rivet Nut: Activate the installation tool. The tool will pull the mandrel back, causing the body of the rivet nut to collapse and flare out on the blind side of the material, creating a strong anchor point.
4. Checking the Installation: The tool will automatically release the mandrel after the rivet nut is set. A properly installed rivet nut will have a visible bulge on the blind side and will be securely fastened in the hole, with the threads ready for a bolt or screw.

Troubleshooting Common Issues

• Rivet Nut Spinning: If the rivet nut spins when you try to insert a screw, it’s likely due to an oversized hole or an improperly set rivet nut. Ensure the hole is the correct size and the installation tool is properly calibrated.
• Incomplete Collapse: If the rivet nut doesn’t fully collapse, the grip range may be too small for the material thickness. Ensure you are using the correct rivet nut for your application.
• Thread Damage: Using the wrong size screw or over-tightening can damage the internal threads. Always use the correct size and torque.

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7. Advantages of Using Blind Rivet Nuts

Blind rivet nuts offer significant advantages over traditional fastening methods like welding or tapping. Their unique design and installation process make them an ideal choice for a variety of applications.

• Creating Strong Threads in Thin Materials: One of the primary benefits is the ability to create a secure, load-bearing thread in materials that are too thin to be tapped. This is particularly useful for sheet metal, plastic, and composite materials.
• One-Sided Installation: Since the installation can be performed from a single side of the workpiece, blind rivet nuts are perfect for applications where access to the blind side is limited or impossible, such as in closed sections or tubes.
• Versatility in Applications: They can be used to join different types of materials, like metal to plastic, and they do not deform or damage the base material, making them suitable for pre-finished or painted surfaces.
• Ease of Use: The installation process is quick and straightforward, and it doesn’t require specialized skills or complex machinery.
• Cost-Effectiveness: While the initial tooling might be an investment, the speed of installation and the reliability of the joint often make blind rivet nuts a more cost-effective solution than welding or other methods in the long run.

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8. Disadvantages of Using Blind Rivet Nuts

Despite their many benefits, blind rivet nuts do have some limitations that must be considered.

• Potential for Spinning if Not Installed Correctly: If the hole is oversized or the rivet nut is not fully set, it can spin when a screw is inserted, making it difficult to fasten. This can be prevented by using the correct tooling and ensuring proper installation.
• Limited Load-Bearing Capacity Compared to Welding: While they create a strong joint, a single rivet nut may not have the same shear or tensile strength as a welded joint. For heavy-duty, high-stress applications, multiple rivet nuts or a different fastening method may be necessary.
• Tooling Costs: For high-volume production, specialized tools like pneumatic or spin-pull riveters are needed, which can be a significant initial investment compared to traditional screws and bolts.

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9. Best Practices for Selecting and Using Blind Rivet Nuts

To ensure the best results and a reliable joint, follow these best practices when working with blind rivet nuts.

• Choosing the Right Type for the Application: Carefully select the rivet nut based on the material (steel, stainless steel, aluminum), body shape (round, hex, splined) for spin-out resistance, and head style (flat, countersunk) for the desired finish.
• Ensuring Correct Hole Size and Preparation: Always drill or punch the hole to the exact diameter specified by the manufacturer. Use a deburring tool to remove any burrs from the hole, which could interfere with proper installation.
• Proper Installation Techniques: Use the correct tool for the job and ensure it is properly calibrated. For critical applications, consider testing the joint strength on a sample piece before full-scale production.
• Regular Inspection and Maintenance: For applications where the fasteners are subject to vibration or repeated stress, periodically inspect the joints to ensure they remain secure.

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10. Blind Rivet Nut Installation Tools

Choosing the right tool is essential for a successful and efficient blind rivet nut installation. The type of tool you need depends largely on the volume of work and the level of portability required.

• Hand Rivet Tools: These are manual tools that use a lever action to pull the mandrel and set the rivet nut. They are ideal for hobbyists, small-scale projects, and occasional repairs. While they are the most affordable option, they require significant physical effort, especially for larger rivet nuts or high volumes.
• Pneumatic Rivet Tools: Also known as air-powered riveters, these tools are designed for high-volume, repetitive tasks on a production line. They are fast, powerful, and reduce operator fatigue. They require a compressed air source and are best suited for industrial environments.
• Electric Rivet Tools: These cordless, battery-powered tools combine the power of pneumatic tools with the convenience and portability of hand tools. They are perfect for on-site installations, field repairs, or any job where an air compressor is not available.
• Spin-Pull Tools: These are specialized tools that not only pull the mandrel but also spin it to ensure a precise and consistent installation. They are often used for critical applications where a perfect set is required.

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11. Common Problems and Solutions

Even with the correct tools and techniques, issues can sometimes arise during installation. Here are some common problems and their solutions.

• Rivet Nut Spinning: This occurs when the rivet nut rotates in the hole when you try to insert a screw.
  • Cause: The hole is oversized, or the rivet nut was not fully set.
  • Solution: Ensure the hole is the correct size. If it’s too late, you can try to “spot weld” the rivet nut in place or use a slightly larger diameter rivet nut if possible. Using a hex body or splined body rivet nut can also prevent this issue in the first place.
• Rivet Nut Pulling Out: This happens when the rivet nut detaches from the material under load.
  • Cause: The grip range of the rivet nut is too small for the material thickness, or the installation was incomplete.
  • Solution: Always select a rivet nut with a grip range that accommodates the thickness of your material. Calibrate your tool to ensure a proper set.
• Thread Damage: The internal threads of the rivet nut are stripped or damaged.
  • Cause: Using a screw of the wrong size, cross-threading, or over-torquing.
  • Solution: Ensure you are using a screw with the correct thread size and pitch. Use a torque-limiting driver to prevent over-tightening. If the threads are already damaged, the rivet nut will need to be replaced.

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12. Conclusion

The blind rivet nut, or nutsert, is a versatile and indispensable fastener that has revolutionized how we create strong, reusable threads in thin materials. Its ability to provide a secure and robust anchor point in applications where traditional methods like welding or tapping are not feasible has made it a cornerstone of modern manufacturing and assembly.

Recap of Key Benefits and Applications

From the automotive and aerospace industries to construction and general manufacturing, blind rivet nuts offer a practical solution for a myriad of fastening challenges. Their key advantages—one-sided installation, creation of strong threads, and adaptability to a wide range of materials—make them a superior choice in countless scenarios. We’ve explored the various types, from round-body to hex-body designs, and the different materials and finishes that allow them to be customized for specific environmental and structural requirements.

Final Thoughts on the Versatility of Blind Rivet Nuts

While some limitations exist, such as a potential for spinning if improperly installed or a lower load-bearing capacity compared to welding, these can be mitigated by following best practices, selecting the right type of rivet nut for the job, and using the correct installation tools. The continuous evolution of installation tools, from simple hand riveters to sophisticated pneumatic and electric tools, has made the process faster, more reliable, and more accessible to a wider range of users.

Ultimately, the blind rivet nut is far more than just a fastener; it is a critical enabling technology that allows for more flexible, efficient, and cost-effective assembly processes. Whether you are a hobbyist working on a small project or an engineer designing a complex industrial machine, understanding and utilizing the power of blind rivet nuts can open up new possibilities for your fastening applications.