Hex Rivet Nut Hole Size Chart
Choosing the correct hole size for hex rivet nuts is essential to ensure a secure, rotation-resistant installation. Unlike standard round-body rivet nuts, hex rivet nuts require specially shaped hexagonal holes or anti-rotation slots to fully utilize their locking features. This page provides a comprehensive Hex Rivet Nut Hole Size Chart in both metric and inch units, along with practical guidance on hole preparation, installation tools, and application tips—helping engineers, fabricators, and technicians make precise, reliable fastener selections for any project.
Metric Hex Rivet Nut Size Chart
| Nut Size | Thread Type | Across Flats (mm) | Recommended Hole Type | Hole Size (mm) | Grip Range (mm) |
| M4 | M4 x 0.7 | 6.35 | Hex Hole | 6.40–6.50 | 0.5–2.0 |
| M5 | M5 x 0.8 | 7.92 | Hex Hole | 8.00–8.10 | 0.5–3.0 |
| M6 | M6 x 1.0 | 8.94 | Hex Hole | 9.00–9.10 | 0.5–3.5 |
| M8 | M8 x 1.25 | 11.10 | Hex Hole | 11.20–11.30 | 0.8–4.0 |
| M10 | M10 x 1.5 | 13.20 | Hex Hole | 13.30–13.50 | 1.0–5.0 |
| M12 | M12 x 1.75 | 15.80 | Hex Hole | 16.00–16.20 | 1.5–6.0 |
Inch Hex Rivet Nut Size Chart
| Nut Size | Thread Type | Across Flats (inch) | Recommended Hole Type | Hole Size (inch) | Grip Range (inch) |
| #10-24 | UNC | 0.312 | Hex Hole | 0.316–0.320 | 0.020–0.100 |
| 1/4″-20 | UNC | 0.375 | Hex Hole | 0.380–0.385 | 0.020–0.130 |
| 5/16″-18 | UNC | 0.437 | Hex Hole | 0.440–0.445 | 0.030–0.150 |
| 3/8″-16 | UNC | 0.500 | Hex Hole | 0.505–0.510 | 0.040–0.180 |
| 1/2″-13 | UNC | 0.625 | Hex Hole | 0.630–0.640 | 0.060–0.250 |
💡 Notes:
- Across Flats refers to the maximum width across the flats of the hex body. The hole must match this to prevent spinning.
- Hole Size should be slightly larger than the across-flats dimension to allow easy insertion without looseness.
- Hex holes can be created using punch dies, CNC machines, or wire EDM, and must maintain dimensional accuracy.
- Grip Range indicates the applicable material thickness the nut can clamp. Ensure it covers the thickness of your workpiece.
A hex rivet nut is a type of fastener specifically designed to provide strong internal threads in thin or soft materials. Its most distinctive feature is its hexagonal outer shape, which allows it to be inserted into a matching hex-shaped hole for excellent anti-rotation performance. Compared to standard round-body rivet nuts, hex rivet nuts offer superior resistance to spinning and loosening, making them ideal for applications where vibration or torque is present.
Structural Features:
- Hexagonal Body: Fits into a hexagonal hole to prevent spinning during installation or use.
- Internally Threaded: Accepts standard bolts or screws for removable fastening.
- Open-End Design: Installed by pulling and deforming the rear portion to clamp onto the workpiece securely.
Typical Applications:
- Metal Structures: Such as sheet metal panels and equipment frames.
- Machinery: In joints that require high resistance to rotation or loosening.
- Automotive Industry: Commonly used in body panels, chassis, and other structural parts.
- High-Vibration or Torque Areas: Like fans, electrical enclosures, and control cabinets.
Hex rivet nuts are widely used in demanding industrial settings where secure, rotation-resistant connections are critical. For optimal performance, it is essential to match the correct hex hole dimensions—refer to the hex rivet nut hole size chart for detailed guidance.
Why Do Hex Rivet Nuts Require Special Hole Shapes?
Hex rivet nuts, due to their hexagonal outer shape, are specifically designed to provide anti-rotation performance, which sets them apart from standard round-body rivet nuts. As a result, they cannot be used with regular round holes. Instead, they must be installed into hexagonal holes or round holes with anti-rotation keying features. Here’s a detailed explanation:
1. Prevent Slipping or Spinning During Installation
- During installation, the tool applies axial force and torque to the rivet nut;
- If inserted into a round hole, the hex-shaped body cannot firmly grip the surrounding material;
- This leads to slippage or spinning, making it impossible to properly deform the body for a secure fit;
- In severe cases, the nut may spin freely, making it unusable.
2. Improved Stability and Reliability
- A hexagonal hole matches the nut’s shape, creating a mechanical interlock;
- This prevents loosening under vibration or load;
- Ideal for high-strength connections or applications involving torque, such as in automotive assemblies, machinery, and structural frames.
3. Better for Frequent Maintenance and Reuse
- The anti-rotation locking effect means the nut remains secure even after multiple bolt installations and removals;
- This makes it suitable for parts that require regular servicing or replacement.
Summary:
The primary reason hex rivet nuts require special hole shapes is to ensure a secure anti-rotation fit between the nut and the base material. Without a hex hole or anti-rotation features, the nut cannot fully perform its function, risking installation failure or future loosening. Therefore, always refer to a Hex Rivet Nut Hole Size Chart to drill the correct hole for safe and effective installation.
How to Drill Hex Holes for Rivet Nuts?
To ensure strong anti-rotation performance, hex rivet nuts must be installed in properly shaped hexagonal holes or round holes with anti-rotation features. Below are common methods for creating hex holes and key considerations:
1. Using a Hex Punching Die
- Best suited for mass production in sheet metal processing (steel, stainless steel, aluminum, etc.);
- Fast operation with standardized hole shapes and high efficiency;
- Typically used for thin metal sheets (1mm–5mm) in conjunction with a punching machine;
- Requires high precision on flat-to-flat dimensions and regular die calibration.
2. CNC Machining or Laser Cutting
- Ideal for metal components and precision parts;
- Allows cutting of hex holes in any size and shape with high accuracy and repeatability;
- Suitable for medium to thick materials (5mm and above) or irregular-shaped workpieces;
- Controlled via CAD programming to ensure dimensional accuracy.
3. Milling Anti-Rotation Slots in Round Holes
- When punching or CNC cutting is not feasible, drill a standard round hole first, then mill one or two small anti-rotation slots along the wall;
- Especially effective for splined rivet nuts, providing a certain level of anti-rotation;
- During installation, ensure the splines or knurls align with the milled slots;
- A good choice for small batches, repair jobs, or on-site work.
4. Importance of Hole Precision
- If the hole is too large, the rivet nut may spin during installation, causing failure;
- If the hole is too small, the rivet nut won’t fit or may damage the base material;
- It is highly recommended to refer to a Hex Rivet Nut Hole Size Chart to determine the correct across flats (AF) dimension;
- For high-load or vibration-prone environments, greater hole precision improves resistance to loosening.
Summary:
Creating a properly shaped and precisely sized hex hole is essential for secure, anti-rotation installation of hex rivet nuts. Depending on the material type, equipment availability, and application needs, choose the most suitable hole-making method to ensure reliable fastening performance.
Can I Use Round Holes for Hex Rivet Nuts?
Although hex rivet nuts are designed to fit hexagonal holes to prevent rotation, in some low-torque, low-load applications, it is possible to install them in round holes. However, in this case, the anti-rotation function may not be fully effective, and there is a risk of the nut rotating, especially in environments with vibration or cyclic loads, where anti-rotation performance can be significantly reduced.
To ensure a secure and reliable installation, it is recommended to prioritize using specially designed hex holes, which fully utilize the anti-rotation advantage of hex rivet nuts. If manufacturing constraints require the use of round holes, mechanical locking features such as small slots or additional fasteners around the hole edges can be added to help improve the anti-rotation effect.
In summary, choosing the proper hole shape and machining method is key to ensuring the long-term stable performance of hex rivet nuts.
Installation Tips and Tools for Hex Rivet Nuts
Use Rivet Nut Tools with Torque Control
Electric or pneumatic rivet nut tools with torque control can precisely manage installation torque, preventing over-tightening that may deform the nut or cause insecure fastening. For example, the recommended torque range for an M6 rivet nut is approximately 5–10 Nm.
Ensure Proper Alignment of the Fixture with the Hole Shape
Hex rivet nuts must be accurately aligned with the hexagonal hole to avoid improper locking or stress concentration. The installation fixture should match the hole shape to prevent the nut from tilting or rotating during installation.
Set Appropriate Pressure When Using Pneumatic or Electric Tools
When using pneumatic rivet nut guns, maintain air pressure typically between 4–6 bar to ensure even installation force without damaging the nut. Excessive pressure may deform the nut or damage the base material, while insufficient pressure can result in loose fastening.
FAQs
1. How Does Temperature Affect Hex Rivet Nut Installation?
Temperature can significantly impact the installation of hex rivet nuts, especially in outdoor, industrial, or specialized environments. Here’s a detailed explanation from multiple aspects:
a. Thermal Expansion Affects Hole Fit
- In high-temperature environments, metal materials (such as steel or aluminum) expand, potentially causing the hole size to increase slightly, which can reduce the fit between the rivet nut and the hole wall, thereby compromising anti-rotation and fastening strength.
- In low-temperature environments, materials shrink, resulting in tighter holes that may make insertion difficult or cause deformation during installation.
It’s recommended to adjust hole dimensions or select materials based on the expected temperature conditions during use.
b. Thermal Deformation of the Nut Body
- Hex rivet nuts are commonly made from carbon steel, stainless steel, or aluminum alloy, each responding differently to temperature:
- Aluminum alloys: Higher thermal expansion rate, more prone to deformation;
- Stainless steel: More stable, but extremely high temperatures can still weaken its structural integrity.
- During high-temperature installation, the nut may soften, leading to poor riveting or loss of deformation capacity.
c. Tool Performance Limitations
- Pneumatic or electric rivet nut tools may experience air pressure fluctuations or battery degradation in low temperatures.
- In poorly ventilated high-temperature areas, tools may overheat and shut down, and operators may find it difficult to control pressure precisely.
Consider using temperature-resistant tools or those with built-in temperature control, and perform regular maintenance.
d. Lubrication and Torque Variation
- Temperature changes affect thread lubrication, which in turn influences tightening torque:
- High temperatures thin out lubricants, possibly resulting in insufficient preload;
- Low temperatures make lubricants more viscous, increasing resistance and the risk of thread damage or under-tightening.
Use torque testing during installation and consider dry film lubricants for better consistency.
e. Thermal Cycling Leads to Fatigue or Loosening
- In environments with frequent temperature fluctuations (e.g., outdoor machinery, vehicle chassis), repeated expansion and contraction can cause:
- Hole wall wear;
- Fatigue failure in the riveted area;
- Rivet nuts becoming loose or rotating.
In such cases, it’s advisable to use stainless steel hex rivet nuts and consider anti-loosening designs or coatings.
2. What Are Common Signs of Improper Hex Hole Size?
Great question—improper hex hole size can significantly impact the performance and reliability of rivet nuts or other fasteners. Here are common signs that a hex hole size is incorrect (either too small or too large):
Signs the Hex Hole is Too Small:
- Difficulty Inserting the Rivet Nut
- Excessive force is required, or insertion is not possible without damaging the fastener or workpiece.
- Distortion of the Workpiece
- The material around the hole bends or deforms during installation.
- Improper Seating of the Rivet Nut
- The flange may not sit flush with the surface, affecting clamping force and appearance.
- Tool Jamming or Damage
- Installation tools may jam, stall, or suffer undue wear due to excess resistance.
Signs the Hex Hole is Too Large:
- Rivet Nut Spins in the Hole (Spin-Out)
- During installation or use, the nut fails to lock in place and rotates freely.
- Reduced Torque Resistance
- The fastened joint loosens under vibration or dynamic load.
- Misalignment or Tilted Fastener
- The rivet nut doesn’t sit squarely in the hole, leading to uneven load distribution.
- Cracked or Split Workpiece
- Lack of proper support may lead to cracks, especially in brittle materials.
- Pull-Out Failure
- The rivet nut pulls through the material under load due to insufficient grip.
Best Practice Tip:
Always refer to the manufacturer’s recommended hex hole dimensions and tolerances for each type of rivet nut or insert. A properly sized hole ensures correct deformation of the knurls or flats, providing superior torque and pull-out performance.
3. Can Custom Hole Sizes Be Manufactured for Specialized Hex Rivet Nuts?
Yes, custom hole sizes can be manufactured to accommodate specialized hex rivet nuts—especially when standard dimensions don’t meet the requirements of your application.
If your project involves large volumes of fasteners, customizing the hole size can be a cost-effective way to improve long-term performance and reduce rework or assembly issues.
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