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Rivet nut
Rivet nut
from Wikipedia
Typical rivet nut
Sectional view
Sectional view, with bolt inserted

A rivet nut, also known as a blind rivet nut, or rivnut,[1] is a one-piece internally threaded and counterbored tubular rivet that can be anchored entirely from one side. It is a kind of threaded insert. There are two types: one is designed to form a bulge on the back side of the panel as a screw is tightened in its threads. The other is similarly drawn in using a screw, but is drawn into the sleeve instead of creating a bulge.[2][3]

History

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The first rivet nut was created by BF Goodrich in the 1930s, and sold under the trademark RIVNUT®. It was first used to mount rubber de-icing boots to aircraft wings.[4]

Usage

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In the field of aviation, rivet nuts are often used to attach various items, such as static dischargers and inspection access covers, to the surface of an aircraft.[citation needed] Rivet nuts are an ideal replacement for weld nuts because they will not distort base materials, eliminate weld splatter, toxic fumes, and other by-products of the welding process, and can be installed in many different kinds of material including steel, plastic, composites, and fiberglass. [5]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia
from Grokipedia
A rivet nut, also known as a blind rivet nut or rivnut, is a one-piece internally threaded tubular fastener designed for blind installation into thin or weak materials, providing a strong, reusable threaded hole for bolts or screws without requiring access to the opposite side. It features a counterbored head and collapsible body that deforms during installation to create a secure mechanical lock, distributing load evenly and preventing distortion in materials like , plastics, or composites. Invented in 1936 by the BF Goodrich Company to attach rubber de-icer extrusions to wings, the rivet nut addressed the need for reliable fastening in inaccessible areas, marking a significant advancement in blind fastener technology. Originally trademarked as RIVNUT®, it has since become a standard component manufactured from materials such as aluminum, steel, and , with thread sizes ranging from unified 4-40 to 1/2-20 and metric M3 to M12, accommodating grip ranges up to 0.450 inches (11.4 mm). The installation process involves a matching the nut's , threading the onto a of a specialized tool, inserting it into the , and applying tension to deform the body, forming a bulge on the blind side for retention. Variations include open-end designs for standard use, closed-end for sealing applications like fuel tanks, and keyed types for enhanced resistance, making nuts versatile for high-vibration environments. Rivet nuts are widely applied in industries such as automotive, , , appliances, boating, and recreational vehicles, where they provide superior shear and tension strength compared to weld nuts or traditional bolts, while allowing easy disassembly and resisting loosening from vibrations. Their blind and ability to join multiple materials without specialized equipment have made them essential for modern assembly processes.

Overview

Definition and Function

A rivet nut, also known as a blind rivet nut or nutsert, is a one-piece, internally threaded, tubular designed to be inserted into a pre-drilled hole in a workpiece and anchored entirely from one side without access to the opposite side. It features a hollow body with internal threading and a counterbored head, allowing it to function as a blind insert that deforms to secure itself in place. The primary function of a rivet nut is to create a strong, reusable threaded hole in materials that are too thin, soft, or brittle for traditional or nut installation, enabling secure attachment of bolts or screws where conventional methods would cause or failure. This makes it particularly valuable for applications requiring reliable fastening in limited-access scenarios, such as joining panels or components without backing support. Key characteristics include its blind installation process, which relies on deformation—typically the formation of a bulging or closing head on the inaccessible side—to grip the material and provide high pull-out strength. Rivet nuts are versatile for use with a range of materials, including metals, plastics, composites, and , accommodating diverse industries like automotive, , and appliances. Originally developed in , the rivet nut was branded as "RIVNUT®" by BF Goodrich for its initial applications in aircraft assembly.

Basic Operation

The basic operation of a rivet nut involves inserting the into a pre-drilled hole in the workpiece and then deforming it using a specialized tool that applies axial pull force via a threaded . This deformation secures the rivet nut in place, creating a strong threaded anchor point accessible from one side. Rivet nuts employ two primary deformation mechanisms to achieve fixation. In the first, compression forms a bulge at the blind end of the rivet nut, where the tubular body collapses inward and expands outward against the far side of the workpiece, creating a mechanical interlock. The second mechanism involves drawing the sleeve portion of the rivet nut into a countersunk or swaged shape at the accessible end, which clamps the material tightly and distributes compressive forces across the hole's perimeter. These processes rely on the plasticity of common materials such as aluminum or , allowing controlled deformation without cracking. Once installed, load distribution occurs as the internal threads of the rivet nut engage with a mating bolt, transferring both and axial forces through the deformed body to the workpiece. The bulged or swaged sections act as anchors, converting rotational and pulling loads into radial and axial compression against the surrounding . This engagement ensures even stress distribution, with the deformed enhancing resistance to shear and tension. The physics of securing relies on radial and axial expansion of the rivet nut, which generates high frictional forces and a mechanical interlock to prevent pull-out or under load. The bulge or swage creates a wedging effect that embeds the into the workpiece, while the threaded interface provides precise transmission without slippage. This dual-action mechanism achieves pull-out strengths typically exceeding 2.4 kN and torque-to-turn values up to 15 Nm for standard sizes, depending on material thickness and type. Installation torque guidelines vary by rivet nut size and material but follow general ranges to ensure proper deformation without over-stressing the . For example, M6 rivet nuts are typically set at 10-15 Nm, with aluminum bodies requiring around 9.5-12 Nm and bodies up to 15 Nm to achieve optimal clamping. Exceeding these values risks thread damage or incomplete setting, while under-torquing may result in insufficient grip.

History

Invention

The rivet nut, commonly known under the trademark , was invented in 1936 by the B.F. Goodrich Company to provide a reliable blind fastening solution for aviation applications. It addressed the critical need for securing components to thin materials like aluminum sheets without requiring access to both sides of the workpiece. The primary purpose of this invention was to attach rubber de-icing boots to the leading edges of aircraft wings, where traditional methods such as welding or soldering proved impractical due to limited access and the risk of damaging delicate structures. The design allowed installation from one side only, forming a strong threaded anchor that could withstand vibrational stresses in flight. This innovation was particularly vital for military aircraft during World War II, enabling efficient assembly in constrained environments. The foundational patent for the rivet nut is U.S. Patent No. 2,149,199, titled "Tubular rivet," filed on August 13, 1936, by inventor Harry E. Waner and assigned to the B.F. Goodrich Company. Granted on February 28, 1939, the patent describes a one-piece tubular device with internal threads, a flanged head, and a deformable body that expands radially upon axial compression to create a secondary flange, thereby locking securely into the parent material. This mechanism overcame prior limitations in blind fasteners by providing high torque resistance and reusability for threaded connections.

Development and Adoption

Following the initial for applications in 1936, rivet nut technology expanded significantly in the post-World War II period as demand grew for reliable blind fasteners in diverse sectors. B.F. Goodrich, the original developer, licensed the RIVNUT® trademarked design to the AVK Corporation, enabling the first and scaling of production beyond uses. This licensing facilitated in the 1950s, with AVK focusing on efficient processes to meet rising industrial needs. Key milestones included widespread adoption in the , where rivet nuts were employed for assembling body panels and attaching thin metal skins to frames, offering advantages in accessibility and strength over traditional nuts and bolts. By the , standardization efforts advanced through organizations like the (ISO) and the (ASME). These standards ensured interoperability and quality consistency, accelerating integration into global supply chains. In the , modern developments introduced high-strength variants optimized for composite materials, addressing challenges in lightweight for and automotive applications. The global market experienced robust growth thereafter, with annual production surpassing millions of units by the to support expanding uses in , appliances, and . Influential companies have driven ongoing innovations, including Bollhoff, which acquired the RIVNUT® business in and expanded U.S. manufacturing; Stanley Engineered Fastening, known for Avdel-brand rivet nuts and pneumatic installation tools; and PEM (PennEngineering), a leader in engineered fasteners that complement rivet nut applications with high-performance variants.

Design and Components

Structure

A rivet nut consists of three primary components: the head, body, and tail. The head, which can be countersunk for flush mounting or flat/large flange for broader bearing surfaces, provides the installation interface and load distribution. The body is a tubular section containing internal threads for mating with bolts or screws, often featuring variations like round, hexagonal, or splined profiles. The tail, located at the opposite end, is the deformable portion that expands during setting to secure the fastener. Standard dimensions for rivet nuts accommodate a range of applications, with thread sizes typically spanning M4 to M12 for metric standards or equivalent imperial sizes such as #8 to 1/2-13 UNC. Body lengths generally vary from 6 mm to 25 mm, depending on the required grip and material thickness. The grip range, which indicates the thickness the can secure, is commonly 0.5 mm to 6 mm, though specialized variants extend to 0.25 mm to 12.7 mm. Engineering features enhance the rivet nut's performance and installation reliability. A or countersunk head allows for flush integration into the parent material, minimizing protrusions. Exterior , splines, or hexagonal body shapes provide anti-rotation resistance by gripping the surrounding material. Internal threads adhere to established standards, such as ISO metric pitches or UNC/Unified coarse threads, ensuring compatibility with standard fasteners. In cross-section, the pre-installation rivet nut appears as a straight, cylindrical tube with a threaded interior, diameter from head to tail, and minimal deformation. Post-setting, the tail deforms outward to form a bulbous or multi-lobed bulge that clamps against the reverse side of the material, while the body may partially collapse to create a tight seal, transforming the overall shape into a secured, expanded profile.

Materials

Rivet nuts are primarily manufactured from , aluminum, and , each selected for specific performance characteristics. Low-carbon , such as grades or 1010, is commonly used for general-purpose applications due to its balance of strength and formability, while variants provide enhanced resistance in harsh environments. Aluminum, often in alloys such as 5056 (5000-series) or 6061 (6000-series), offers lightweight construction ideal for weight-sensitive uses, and , a copper-zinc , is employed where electrical conductivity and resistance are required. Key material properties include tensile strength, , and compatibility with parent materials. Steel rivet nuts can achieve tensile strengths up to 800 MPa in Grade 5 variants, providing robust load-bearing capacity, with typically in the 25-34 HRC range for . Aluminum exhibits lower tensile strength but superior strength-to-weight ratio and inherent resistance, while offers moderate strength with high electrical conductivity. Compatibility considerations, such as using aluminum rivet nuts in assemblies to prevent with similar workpieces, ensure long-term integrity. Coatings and finishes enhance performance against . Zinc on provides protection, with yellow or clear variants offering 50-100 hours to red rust and zinc-nickel exceeding 1,000 hours under ASTM B117 testing; passivation is applied to for improved surface resistance. Polymer coatings, such as PVC or Raintite, are used on for added and barrier properties. Material selection is guided by environmental factors, including temperature extremes from -55°C to 200°C for aluminum 6061-T6 and -55°C to 800°C for 316L, as well as exposure to chemicals or that demand high resistance. excels in chemical-laden settings due to its passivation layer, while aluminum suits non-corrosive, lightweight needs, and is chosen for conductive or decorative applications in mild conditions.

Types and Variants

Standard Rivet Nuts

Standard rivet nuts consist of a cylindrical body with uniform internal threads, providing a reliable blind fastening solution for attaching components to or where only one-sided access is available. The design features a counterbored tubular structure that deforms during installation to create a strong mechanical interlock with the parent material, accommodating standard bolt sizes for subsequent assembly. These fasteners are typically available in materials such as aluminum, , and to suit various environmental and load conditions. Common specifications include unified thread sizes from #6-32 to 3/8-16 UNC and metric threads from M5 to M10, with grip ranges varying by material thickness, often from 0.5 mm to 6 mm for standard applications. Load ratings for these rivet nuts generally provide shear strengths of 500-2000 and pull-out (tensile) strengths of 1000-5000 in typical configurations, ensuring sufficient performance for non-critical loads without requiring specialized tooling. For instance, a #10-32 rivet nut can achieve approximately 3330 shear and 4830 pull-out strength, depending on grip and . Aerospace-grade versions adhere to standards such as NASM 1312-13 for double shear testing and NAS 1329/1330 for dimensional and material requirements, while general industrial types typically comply with quality systems like ISO 9001 and for automotive applications. These rivet nuts are particularly suited for low-to-medium applications, such as panel mounting in automotive assemblies, electronic enclosures, and furniture construction, where their round body design allows for straightforward installation in round holes and provides balanced load distribution without the need for high-precision alignment.

Specialized Types

Specialized types of rivet nuts are engineered variations designed to address specific challenges such as rotation resistance, environmental sealing, high structural loads, and installation in thin or composite materials. These adaptations modify the body shape, sealing mechanisms, or deformation patterns to enhance performance in demanding applications, while maintaining the core blind installation principle. Hexagonal rivet nuts feature a multi-lobe, six-sided body that embeds into the to prevent spin-out, particularly in soft or low-density substrates like aluminum or plastics. This provides superior torque-to-turn resistance compared to standard round bodies, making them ideal for high-vibration environments. For instance, the High Strength Hexsert® from Stanley Engineered Fastening offers clamp forces equivalent to weld nuts, with thread proof loads matching tapped s in soft metals. Similarly, Bollhoff's HEXNUT® installs into a pre-punched hexagonal for enhanced rotational stability. Sealed or splash-proof rivet nuts incorporate , closed ends, or integrated seals to achieve watertight or IP-rated against , oils, and contaminants, which is essential for automotive, marine, and outdoor applications. These variants prevent fluid ingress through the , safeguarding underlying components from . Sherex's watertight rivet nuts, for example, provide robust sealing against water and viscous fluids in harsh environments. Bollhoff's RIVKLE® Seal Ring uses a captive for reliable , while PEM's Deform-Nut® IP68 series features a seal and closed barrel for full in thin panels. Heavy-duty rivet nuts are constructed with thicker walls and reinforced structures to withstand extreme pull-out and shear forces in structural assemblies, such as frames or heavy machinery. These variants prioritize load-bearing capacity, often achieving tensile strengths far exceeding standard types. Sherex's large-size full hex rivet nuts, for instance, demonstrate pull-out strengths over 30,000 pounds in testing, suitable for high-stress fastening. McMaster-Carr's heavy-duty hex models include large head flanges and thick collapse chambers for added strength in demanding scenarios. Splined rivet nuts employ a or grooved body to improve grip and resistance in thin sheet materials, enabling secure installation in panels as low as 0.5 mm thick without limitations. This design distributes stress evenly, reducing the risk of material deformation during torquing. Northern Precision's flat head splined body nuts are available in and for such thin applications. Rivets Online's K-series features a splined structure that enhances twist resistance over non-splined inserts in low-profile setups. Peel-type rivet nuts facilitate rapid deformation for quick installation in composite materials, where the peels away segments of the body to create a broad bearing surface without cracking brittle substrates. This variant supports multi-material joining, including plastics and fiber-reinforced polymers. Bollhoff's RIVKLE® SFC series is specifically developed for such composites, offering peel-type deformation for reliable anchoring. Stanley Engineered Fastening's catalog includes peel-type options compatible with thin composites for vibration-resistant threads.

Installation Methods

Tools and Equipment

Manual rivet nut setters are essential for low-volume or field installations, featuring ergonomic designs with chucks that securely grip the rivet nut during setting. These hand tools typically accommodate thread sizes from M3 to M8, allowing users to install standard rivet nuts in materials up to several millimeters thick without requiring external power sources. Power tools enhance efficiency for higher-volume production, including pneumatic setters that operate at 90-100 to deliver consistent pulling force via . Hydraulic and battery-powered variants provide precise control, with hydro-pneumatic models combining air drive and hydraulic amplification for reliable performance in demanding applications. Accessories play a critical role in tool versatility, such as interchangeable nosepieces tailored to specific thread sizes like M5 to M12, ensuring proper alignment and fit during installation. Mandrels facilitate the pulling action to deform the rivet nut, while advanced models incorporate spin-out detection mechanisms to prevent incomplete settings and alert operators to errors. Key specifications for these tools include stroke lengths of 5-10 mm to accommodate various material thicknesses, and pulling force outputs reaching up to 20 kN for robust deformation without damaging the . Compatibility with established systems, such as those from Astro Pneumatic or Bollhoff, ensures seamless integration and adherence to industry standards for reliable rivet nut installation.

Step-by-Step Process

The installation of a rivet nut begins with proper preparation of the workpiece to ensure secure fastening. Drill a hole in the parent material to match the specified diameter for the rivet nut size, typically with a slight oversize for clearance, such as 0.01 mm larger than the nominal diameter for an M6 rivet nut (e.g., 9.01 mm hole for a 9.0 mm nominal). Deburr the edges of the hole to remove any sharp burrs or debris that could interfere with insertion or setting. The core installation procedure involves the following sequential steps using a dedicated rivet nut installation tool:
  1. Thread the tool's into the internal threads of the rivet nut until secure.
  2. Insert the rivet nut into the prepared hole from the access side of the workpiece, ensuring it sits flush against the surface.
  3. Apply a controlled pull force using the tool to deform the of the rivet nut, expanding its body radially behind the while the tool counters the head to form a clench.
  4. Release the tool by reversing the and inspect the installation for a flush fit of the head against the surface and intact internal threads.
Post-installation quality checks are essential to verify the rivet nut's performance. Test the assembly for pull-out strength by applying axial force within the specified grip range, and evaluate thread torque by inserting a mating fastener and measuring resistance to ensure it meets design requirements, such as torque-to-turn values outlined in manufacturer data. Common errors during installation include over-torquing the mandrel, which can damage the internal threads, and misalignment due to imprecise hole positioning; these can be mitigated by conducting pilot tests to determine optimal torque settings and using pilot holes or fixtures for accurate alignment.

Applications

Industries

Rivet nuts are extensively utilized in the aerospace industry, particularly in airframes for attaching panels and avionics, where their lightweight construction and ability to facilitate one-sided access are essential for maintaining structural integrity in confined spaces. In aircraft fuselages and cockpits, they secure non-critical components such as cabin panels and overhead compartments, contributing to overall weight reduction for improved fuel efficiency. In the automotive sector, rivet nuts play a key role in fastening interior trim, body panels, and exhaust components during high-volume assembly lines, enabling efficient joining of thin materials without requiring access to both sides. They are commonly employed to secure brackets and heat shields in exhaust systems, as well as to mount trim elements and panels, supporting rapid production processes. The relies on rivet nuts for securing enclosures and circuit boards within housings constructed from plastic or thin metal sheets, providing reliable threaded anchors in applications where space constraints limit traditional fastening methods. These fasteners are ideal for mounting sensitive components like printed circuit boards and battery compartments, ensuring stable connections in compact electronic assemblies. In the appliance industry, rivet nuts are used to assemble components of devices such as refrigerators, washers, and ovens, where they provide strong threaded connections in thin or housings, facilitating durable assembly and serviceability. Recreational vehicles (RVs) employ rivet nuts for mounting interior panels, storage brackets, fixtures, and door hinges in van and RV builds, offering blind installation in thin metal walls and composites to support modular and customizable setups. In construction and marine environments, rivet nuts are applied to join thin sheets in HVAC ducts and boat fittings, with materials selected for their corrosion resistance to withstand exposure to moisture and harsh conditions. variants are particularly valued in marine settings for securing deck hardware and structural fittings on vessels, while in construction, they provide durable anchors in ductwork for ventilation systems.

Specific Uses

In aviation, rivet nuts are employed to secure static dischargers, also known as , to aircraft wings, where they help dissipate buildup during flight to prevent interference with . These fasteners provide a reliable threaded connection in thin or composite materials, allowing for easy installation from one side without compromising structural integrity. Similarly, rivet nuts attach access covers to fuselages, enabling maintenance personnel to remove panels for routine checks while ensuring a secure, vibration-resistant fit in high-stress environments. In the automotive sector, rivet nuts serve as replacements for weld nuts in door hinge assemblies, offering a strong, removable threaded anchor in thin steel panels that withstands repeated door cycles and dynamic loads. This application is particularly valuable in repair scenarios or modular designs where welding is impractical. For interior components, rivet nuts facilitate the attachment of plastic dashboards to underlying metal frames, providing precise alignment and load distribution for screws that secure trim panels without distorting the material. Rivet nuts function as threaded inserts in electronics manufacturing, notably for battery compartments in consumer devices such as laptops, where they create durable mounting points in plastic or thin metal housings to hold battery packs securely against vibration and thermal cycling. This ensures reliable electrical connections and easy disassembly for maintenance or upgrades, common in compact assemblies like portable computing hardware. Beyond these sectors, rivet nuts aid in repairing fiberglass boat hulls by embedding studs or threads into composite layers, allowing for the attachment of hardware like cleats or railings without through-bolting that could weaken the structure. In modular furniture assembly, they enable hidden fasteners that join wood or metal frames discreetly, supporting adjustable shelving or tabletops with concealed screw access for a clean aesthetic and tool-free reconfiguration.

Advantages and Limitations

Benefits

Rivet nuts offer significant advantages in blind accessibility, allowing installation from only one side of the workpiece, which makes them ideal for hollow structures, tubular components, or areas where the opposite side is inaccessible or obstructed. This one-sided installation eliminates the need for tools or personnel to access the blind side, streamlining assembly processes in applications such as automotive frames or panels. Their versatility enables use across a wide range of materials, including metals, plastics, , and composites, without requiring pre-threading, , or other preparatory steps that could damage delicate substrates. This adaptability reduces setup time and allows rivet nuts to serve as a direct replacement for weld nuts or tapped holes in diverse environments, from field repairs to high-volume production lines. In terms of strength and reusability, rivet nuts provide high pull-out and resistance that often exceeds the tear-out strength of the when properly installed, ensuring a secure, load-bearing threaded connection. For instance, a 1/4-20 rivet nut in 0.030-inch rolled steel can achieve a pull-out strength of 480 pounds, surpassing the sheet's capacity in many scenarios. The internal threads also support multiple bolt insertions and removals without compromising integrity, facilitating maintenance and adjustments. Cost efficiency is another key benefit, as rivet nuts lower labor costs through faster installation—typically quicker than or bolting methods—while minimizing scrap from heat distortion or excessive deformation. By avoiding the need for expensive equipment and skilled welders, they can reduce overall assembly expenses, making them particularly advantageous in where time savings accumulate.

Drawbacks and Considerations

Rivet nuts exhibit reduced strength when installed in very thin materials under 0.5 mm, where the grip range may not fully engage, leading to lower pull-out resistance, although specialized types can accommodate down to 0.25 mm with adjusted performance. Similarly, in thicker materials exceeding 6 mm, standard rivet nuts may deform incompletely or provide diminished clamping force, though extended-grip variants extend up to 12.7 mm at the potential cost of overall joint integrity. Additionally, under extreme , the internal threads of rivet nuts are susceptible to stripping, as measured in torque-out tests where failure occurs when applied exceeds the nut's thread strength, often before the mating bolt shears. Installation challenges include the need for precise hole sizing, with tolerances typically specified as +0.1/-0 mm to ensure a secure fit; deviations can result in a loose installation that compromises load-bearing capacity or causes misalignment. Tool dependency further complicates low-volume applications, as dedicated manual or pneumatic tools, costing several hundred dollars, are required for proper crimping, elevating initial setup expenses compared to simpler fastening methods. Key considerations encompass environmental factors such as , which can induce loosening of the mating within the nut's threads over time; this is commonly mitigated by applying threadlocking compounds that create a to resist rotational movement. poses another challenge when nuts introduce mixed materials, such as a nut in an aluminum sheet, complicating material separation and potentially contaminating sorted streams during end-of-life processing. In comparison to alternatives, rivet nuts are preferred over self-tapping screws for applications demanding higher load capacities and reusable threaded connections, particularly in thinner sheets where self-tapping options risk material displacement and reduced holding power. Relative to clinch nuts, rivet nuts suit scenarios requiring one-sided access or field repairs in thinner materials, whereas clinch nuts excel in thicker sheets with two-sided installation for enhanced flush integration and stability under high stress.

References

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