Sheet Metal Fasteners: An Engineer’s Guide

Sheet metal fabrication presents a distinct set of joining challenges that are not fully addressed by welding alone. While welding offers a permanent and structurally robust solution, it is not always practical. It requires specialist equipment and skills, introduces heat that can distort thin sheet material and produces a joint that cannot be easily undone. 

In assemblies that require periodic disassembly for maintenance, adjustment or inspection or where heat-affected distortion cannot be tolerated, sheet metal fasteners offer a more flexible and often more appropriate solution.

Selecting the wrong fastener for sheet metal can introduce problems as significant as the joining challenge it was intended to solve, like stripping threads, accelerating corrosion or simply being impossible to install reliably under the conditions the assembly demands. 

This practical, engineer-led guide examines the best fasteners for sheet metal applications, covering the key considerations that influence selection, a comparative table for at-a-glance reference and an FAQ section addressing the most common questions around sheet metal fastening in practice.

Contents:

• What to Consider When Joining Sheet Metal

• What Are the Best Types of Sheet Metal Fasteners?

• Which Types of Sheet Metal Fasteners Should I Use?

• Key Takeaways for Using Sheet Metal Fasteners

• FAQs

What to Consider When Joining Sheet Metal

Selecting the right fastener for a sheet metal application is rarely as straightforward as choosing a component that physically fits the joint. The specific requirements of the assembly all place constraints on which fasteners are viable and ignoring any one of them can introduce failure modes that are difficult and costly to resolve. 

In practice, these considerations interact with one another and a decision made in response to one constraint will often have implications for others, making them the essential starting point for identifying which of the sheet metal fastening methods covered in this guide are best suited to the job.

 

Sheet Metal Material

The material from which the sheet metal has been fabricated is one of the most fundamental considerations in fastener selection and one that must be addressed before any other specification decision is made.

Choosing a fastener for sheet metal that is mechanically appropriate but materially incompatible with the substrate can introduce failure modes that are entirely avoidable, the most significant of which is galvanic corrosion.

Galvanic corrosion occurs when two dissimilar metals are placed in contact in the presence of an electrolyte, most commonly moisture. When this happens, the less noble of the two metals acts as an anode and begins to corrode preferentially. 

In a sheet metal assembly, this process concentrates at the interface between the fastener and the sheet, which is precisely where structural integrity is most critical. The result is accelerated material loss at the joint, which can compromise clamping force, cause staining of the visible surface and, in severe cases, lead to joint failure well ahead of the assembly's expected service life.

Where possible, fastener material should be matched to the workpiece substrate. For example, stainless steel self-drilling screws are well-suited to joining stainless steel sheet metal, offering both material compatibility and the corrosion resistance required for demanding environments. For aluminium sheet metal, aluminium pop rivets or appropriately coated steel fasteners are preferable to uncoated steel.

Where material matching is not possible due to availability, cost or mechanical constraints, the risk of galvanic corrosion can be managed through the use of insulating washers, barrier coatings or sealants that prevent direct metal-to-metal contact at the joint, such as thread lockers.

However, these add complexity to the assembly process and introduce additional components that must be correctly specified and consistently applied. Selecting compatible materials from the outset remains the more reliable approach.

It is also worth noting that the relative surface areas of the two metals in contact influence the rate of galvanic corrosion. A small fastener of a less noble metal in contact with a large sheet of a more noble metal will corrode rapidly, as the anodic area is small relative to the cathodic area. This makes fastener material selection particularly consequential in sheet metal assemblies, where the fastener is almost always the smaller of the two components in contact.

 

Sheet Metal Thickness

Sheet metal by its nature occupies a relatively narrow thickness range and within that range, small differences in gauge can determine whether a fastener will grip reliably, strip the material entirely or fail to engage at all.

The most immediate challenge presented by thin sheet metal is the inability to support a traditionally drilled pilot hole and tapped thread. The thinner the sheet, the fewer thread engagements are available. Below a certain thickness, there is simply not enough material present to form a stable threaded connection using conventional methods. Attempting to drive a standard machine screw into sheet metal that is too thin to support it risks stripping the material on the first installation, leaving a fixing point that cannot be relied upon.

Self drilling bolts and screws are specifically designed to address this constraint. Their drill-point tip cuts through the sheet without requiring a pre-drilled pilot hole, while the thread form is optimised to engage thin material without deforming or stripping it. This makes them one of the most practical and widely used fasteners for sheet metal applications across a broad range of gauges, eliminating a separate drilling operation and reducing the risk of misalignment between the pilot hole and the fastener.

Where a reusable threaded fixing point is required in thin sheet metal, for example, in an assembly that will be regularly disassembled for maintenance, rivet nuts and clinch nuts, which are often called self-clinching fasteners, offer a reliable solution. Rather than relying on the sheet material itself to carry the thread, these fasteners introduce a threaded insert that is mechanically retained within the sheet. 

In practice, a rivet nut is installed into a pre-drilled hole and set using a tool that deforms its body against the reverse face of the sheet, distributing the load over a larger bearing area than a tapped hole in the sheet alone could provide. Similarly, clinch nuts are pressed directly into the sheet under force, with their knurled or hexagonal body displacing material to create a secure, non-rotating fixing point.

At the thinner end of the sheet metal gauge range, even the installation forces involved in setting a rivet nut or driving a self drilling screw can be sufficient to deform or buckle the workpiece if the process is not carefully controlled. In these cases, pop rivets can offer a lower-installation-force alternative for permanent joints, as the setting process places less localised stress on the surrounding material than thread-forming operations.

 

Hardness and Ductility

The hardness and ductility of the sheet metal substrate are distinct but closely related considerations. Both have a direct bearing on which fasteners are viable for a given application. 

Ductility governs the sheet metal's ability to deform without fracturing. When a thread-forming fastener is driven into sheet metal, the material around the fastener is displaced rather than removed, creating a formed thread that grips the fastener body. This process places localised stress on the material immediately surrounding the fixing point.

Where ductility is inadequate, as can be the case with hardened, heavily cold-worked or brittle sheet materials, thread-forming operations can initiate cracks at the fixing point that propagate through the surrounding material, causing damage that is not always immediately visible but that significantly weakens the joint.

Self tapping screws rely on this thread-forming process and are well-suited to sheet metals with adequate ductility, such as mild steel, aluminium alloys and annealed stainless steel. However, in materials that are at the harder or less ductile end of the spectrum, thread-cutting variants are a more appropriate choice.

Hardness introduces a separate but related constraint. Where the sheet metal is harder than the fastener itself, the fastener may deform or fail before it can cut or form a thread. This is particularly relevant when using self drilling screws, whose drill-point tip must be capable of penetrating the sheet. Self drilling screws are rated for use within specific material hardness ranges and specifying a fastener outside of that range risks tip failure, workpiece damage or an incomplete fixing point that cannot be relied upon structurally.

Where the hardness or brittleness of the sheet metal makes thread-forming or thread-cutting operations impractical, fasteners that do not rely on engaging the sheet material directly offer a more reliable alternative. 

Weld studs bypass the material constraints of thread-forming entirely by fusing a threaded stud directly to the surface of the sheet, creating a permanent fixing point without any drilling, cutting or forming operation. This makes them particularly well-suited to harder sheet materials where other fastening methods would risk damaging the workpiece, provided that welding is compatible with the assembly process and material.

Similarly, pop rivets and rivet nuts avoid the thread-forming process altogether. Both are installed through a pre-drilled clearance hole, placing no thread-forming load on the surrounding material and making them suitable for a wider range of sheet hardness values than screw-based fasteners that rely on engaging the substrate directly.

 

Load Requirements

Sheet metal assemblies can be subjected to a wide range of loading conditions, from static clamping loads to dynamic, cyclic stresses. The consequences of specifying a metal sheet fastener that is inadequate for the loads it will experience range from gradual performance degradation to sudden and complete joint failure.

Vibration Resistance

Vibration is one of the most common and demanding load conditions encountered in sheet metal assemblies, particularly in automotive, aerospace and industrial machinery applications. Cyclic loading caused by vibration places repeated stress on the fastener and its engagement with the sheet. Fasteners that rely solely on thread friction for retention can loosen progressively over time as this preload is gradually reduced. 

Weld studs offer one of the most effective solutions to vibration-induced loosening in sheet metal assemblies. By fusing directly to the surface of the sheet, they create a permanent fixing point that cannot rotate or back out under cyclic loading. Where a permanent joint is appropriate and the assembly process supports welding, weld studs are a reliable choice for high-vibration environments. 

It’s worth noting that, if you’re using weld studs in a high vibrational application, the fastener that they are paired with will also require a means to resist vibrational loosening. Thread lock is a common solution to this problem, as are anti-vibration safety washers.

Rivet nuts and clinch nuts similarly resist rotation within the sheet once installed, providing a stable threaded fixing point that maintains its integrity under sustained vibration even as the mating fastener is repeatedly installed and removed.

Tensile Load

Tensile load, the force acting to pull the fastener directly out of the sheet, is another key consideration that can significantly narrow the range of viable fasteners. In thin sheet metal, the bearing area available to resist tensile load is limited. Fasteners that concentrate load at a single point can pull through the sheet under sustained or impact loading. 

Rivet nuts distribute tensile load over a larger bearing area than a tapped hole in the sheet alone, making them better suited to joints where pull-out resistance is a stated requirement. For the highest tensile load applications, clinch nuts and other self-clinching fasteners pressed into the sheet provide a similarly robust solution, with their knurled or hexagonal body mechanically interlocked with the surrounding material to resist both pull-out and rotation.

Shear Load

Shear load, acting parallel to the sheet surface rather than perpendicular to it, places different demands on the joint. Pop rivets are well-suited to shear-loaded joints in sheet metal as their body fills the drilled hole and bears directly against the sheet material on both faces, distributing the load effectively across the joint. However, their relatively modest tensile pull-out resistance means they are less appropriate where combined shear and tensile loads are present simultaneously.

 

Assembly and Functional Considerations

The practical realities of assembling a sheet metal workpiece can be just as influential on fastener selection as its mechanical requirements. Even a fastener that is perfectly specified for the material, thickness and load profile of an assembly can introduce significant difficulties if it is poorly suited to the conditions under which it must be installed or the function it must support once in service.

One of the most common challenges in sheet metal work is restricted access and working in a confined space. Sheet metal assemblies are frequently enclosed, panelled or integrated into larger structures in ways that limit or entirely prevent access to the reverse face of the joint. 

In these situations, fasteners that require two-sided installation, such as a traditional nut and bolt arrangement, become impractical regardless of their mechanical suitability. Attempting to install them anyway introduces the risk of dropped components within the assembly, which in regulated industries such as aerospace, electronics and precision machinery can be classified as Foreign Object Debris (FOD). 

A loose fastener left inside an enclosed assembly can cause mechanical damage, electrical faults or premature wear if it migrates during operation, and retrieving it may require significant disassembly and rework.

Where FOD risk is a primary concern, captive screws offer a practical solution. Mechanically retained within their mating panel or housing, they cannot be fully removed and therefore cannot be dropped or lost during installation or maintenance, making them particularly well-suited to enclosed assemblies in regulated industries. They can also be paired with a captive washer to ensure secure fastening and component retention. 

Pop rivets and rivet nuts address the one-sided access problem directly. Sheet metal rivets like these are installed entirely from the front face of the sheet with no requirement for access or fixturing on the reverse side. Pop rivets provide a permanent, one-piece joint that eliminates loose components entirely, while rivet nuts create a reusable threaded fixing point from a single-sided installation. This makes them ideal for assemblies that will need to be disassembled and reassembled in service. 

Visibility and dexterity compound these challenges further. Fastener locations within enclosed or partially assembled workpieces may be obscured by surrounding components or awkward viewing angles, requiring installation by feel rather than sight. Where personal protective equipment is also required, like gloves, face shields and bulkier protective clothing, the risk of cross-threading, incomplete engagement or dropped components increases. 

In these conditions, self drilling screws reduce the installation process to a single operation, removing the opportunity for misalignment between a separate drilling and fastening step. Where tool access is restricted, hex or socket drive fasteners allow torque to be applied laterally, making them more forgiving of the off-angle approaches that confined or visually restricted installations often demand.

 

What Are the Best Types of Sheet Metal Fasteners?

 

There is no single fastener that can be described as the best option for sheet metal applications. The considerations outlined above are designed to narrow the field before a final selection is made. 

Once those constraints are understood, the table below provides a concise, at-a-glance reference for identifying the most appropriate fastener for a given application, covering the key advantages and limitations of each type and the conditions under which each one is and is not appropriate.

 

 

Which Types of Sheet Metal Fasteners Should I Use?

The comparison table above offers a detailed breakdown, but the guide below provides a quick way to narrow down your selection based on the primary requirement of your project.

• For high-speed installation without pre-drilling: Self drilling screws (often called TEK screws) are ideal as they eliminate the need for a separate pilot hole operation, saving time in high-volume assemblies.

• For creating a reusable thread where you only have access to one side: Rivet nuts are the best choice. They are installed from the front face and provide a robust internal thread for standard machine screws in thin material.

• For a permanent, low-profile joint with one-sided access: Pop rivets offer a reliable, vibration-resistant solution that is quick to install and eliminates the risk of loose components (FOD).

• For maximum pull-out and rotation resistance in thin sheets: Hexagon clinch nuts and self-clinching fasteners are pressed into the sheet, mechanically interlocking with the material to provide a high-strength threaded fixing point that stays flush with the surface.

• For outdoor or weatherproof applications: Roofing screws (TEK screws with EPDM washers) should be used to create a watertight seal at the fixing point, preventing moisture ingress.

• For high-vibration environments where the fastener must never loosen: Weld studs are fused directly to the metal surface, creating a permanent fixing point that is immune to vibration-induced loosening.

• For restricted access or regulated environments where dropping parts is a risk: Captive screws are mechanically retained within the panel, making them perfect for assemblies that require frequent maintenance without the risk of losing hardware.

 

Key Takeaways for Sheet Metal Fastening

• There is no single best fastener for sheet metal. The right choice depends on material, thickness, load profile, environment and assembly conditions.

• Material compatibility is the first consideration. Mismatched metals introduce galvanic corrosion risk that coatings and treatments alone may not reliably resolve.

• Self drilling and self tapping screws are among the most versatile options, but both are rated for specific material hardness ranges and must be specified accordingly.

• One-sided access is a common constraint in sheet metal assemblies. Pop rivets and rivet nuts are specifically designed to address it.

• Permanent joints are not always the right solution. Where disassembly is anticipated, rivet nuts and clinch nuts provide robust, reusable threaded fixing points in thin sheet.

• Fastener selection should account for the full service life of the assembly, not just the requirements of the initial installation.

Sourcing Sheet Metal Fasteners

Selecting the right fastener for a sheet metal application is only part of the equation. Consistent results also depend on sourcing components that meet the exact material, dimensional and drive requirements of the assembly, particularly where sheet gauge tolerances are tight, environmental conditions are demanding or rework is costly.

Accu stocks over 500,000 precision components, including the full range of fasteners covered in this guide, so whatever the specification demands of the job, there are components to suit. If you're unsure which fasteners are right for your application, our team of engineers are on hand to advise and help make sourcing the right components straightforward, reliable and fast.

 

FAQS:

Q: What is the best way to attach something to sheet metal?

A: While welding is often the first method considered for joining sheet metal, it is frequently not the most practical option. It requires specialist equipment and trained operators, is time-consuming relative to mechanical fastening, and introduces heat that can warp or distort thin sheet material. Crucially, it also produces a permanent joint, making it unsuitable for any assembly that requires disassembly for maintenance, adjustment or inspection.

Mechanical fasteners address all of these limitations. They can be installed quickly with standard tooling, place no heat into the material and, depending on the fastener chosen, can produce either a permanent or a removable joint. 

For straightforward through-fastening without a pre-drilled pilot hole, self drilling screws are among the most practical and widely used options. Where one-sided access is unavailable and a permanent joint is acceptable, pop rivets offer a fast, clean solution. Where the joint must remain removable, rivet nuts provide a reusable threaded fixing point installable from one side. 

In all cases, the material, thickness and load profile of the assembly should inform the fastener choice before any other consideration.

 

Q: What are the three types of fasteners used to join sheet metal?

A: While there are more than three fastener types used in sheet metal work, the most commonly referenced categories are screws, rivets and threaded inserts. 

Screws, including self drilling and self tapping variants, are used for through-fastening and are available in a wide range of head profiles and drive types to suit different installation conditions. 

Rivets, including pop rivets and rivet nuts, are used where one-sided access is required or where a permanent joint is appropriate. 

Threaded inserts, such as clinch nuts and rivet nuts, are used to introduce a robust, reusable threaded fixing point into sheet metal that is too thin to support a traditionally tapped thread.

 

Q: What is the best way to attach sheet metal to sheet metal?

A: The most appropriate method for joining sheet metal to sheet metal depends on whether the joint needs to be permanent or removable and whether access to both faces of the assembly is available. 

• For permanent joints where one-sided access is required: Pop rivets are a practical and widely used solution. 

• Where the joint must remain removable: Self drilling screws offer a fast, reliable fixing without a separate pilot hole operation. 

• In high-vibration environments: Weld studs provide a permanent fixing point that cannot loosen in service. 

• For assemblies where load distribution across thin sheet is a concern: Rivet nuts or clinch nuts introduce a threaded fixing point that spreads tensile load over a larger bearing area than a tapped hole in the sheet alone could provide.

 

Q: What are TEK screws and are they suitable for sheet metal applications?

A: TEK is a trade name that has become widely used as a generic term for self drilling screws. These are fasteners with a drill-point tip that cuts through sheet material before the thread engages, eliminating the need for a pre-drilled pilot hole. The name originates from the Buildex TEK screw, but is now commonly applied to self drilling screws across a range of head profiles and materials. 

The appropriate TEK screw for a given application depends on the sheet gauge, material hardness and the specific demands of the installation environment.