Introduction
In manufacturing, the joining of sheet metal parts is a crucial process that is used in various industries such as automotive, aerospace, and many others. But what defines the strength and stability of these assemblies? The fasteners. Selecting the right fastener is not only about joining components but it also determines product reliability, performance, cost, time, and ease of assembly.
A wrong choice of fastener can result in expensive failures, time consumption and even dangerous products. On the other hand, a proper selection of a fastener that is the best fit when properly applied provides a perfect, long-lasting and economical joint.
This guide offers an introduction to the most common sheet metal fabrication fasteners, examines the critical selection criteria, presents typical uses, introduces professional fastening solutions, explains how to install fasteners properly, and prepares professionals to make the right fastening choices.
What is a sheet metalfastener?
A sheet metal fastener is a fastener that is used to join two or more thin metal sheets that are defined to have a thickness of between 0.5mm and 6mm. Unlike the fasteners designed for thick sections or massive materials are different, the sheet metal fasteners have to overcome the difficulties of thin materials. These are the material deformation under load, the restricted engagement of the thread in thin sections, and the pull through or stripping if excessive force is applied. Hence, sheet metal fasteners have certain design characteristics that allow for load distribution, provide anchoring points within the thin gauge material, or accommodate installation where access may be restricted to one side only. Their role is to provide a strong and permanent connection that will be able to withstand the loads that are expected to be applied to it, and also be easily serviceable if needed.
Key Types of Sheet Metal Fasteners
The variety of sheet metal applications necessitates diverse fastening solutions. It is crucial to understand the main categories to be able to select the most suitable one.
Self-Clinching Fasteners
Self-clinching fasteners are a type of fasteners that are intended to become a part of the type of sheet metal part in which they are used. Some of the most popular ones are self-clinching nuts, studs, and standoffs. Installation entails driving the fastener into a hole of the right size with the use of a parallel-acting press. In this process, the knurled clinching ring or a specially profiled head of the fastener forces the host sheet metal material aside and makes it cold flow into an annular recess or undercut in the shank or pilot of the fastener. This displaced material effectively immobilizes the fastener and offers high resistance to push-out and torque-out forces.
Some of the benefits include the ability to produce strong, permanent fastening or attachment points in thin gauges, good for applications that require high strength in the joint, and the ability to install on one side only. One of the major conditions is the ability to access both sides of the sheet during the installation and the proper press equipment to apply the right seating force and parallelism. They are commonly used in electronics housing, automotive parts, and aerospace industries.
Rivets
Riveting is one of the earliest and most effective ways of joining two or more pieces of sheet metal together due to its ease of use. A rivet is simply a cylindrical shaft with a head on one end of it. Installation involves passing the rivet shaft through holes in the parts to be joined and then expanding the tail end of the rivet to form a second head, the “shop head” or “buck-tail”, by mechanical means. This secures the sheets tightly in place against each other.
- Solid Rivets: Offer the highest shear strength but can only be installed from both sides of the sheet, one side for the manufactured head and the other for the shop head using a hammer and bucking bar or riveting machine, as the solid shaft provides additional support during installation.
- Semi-Tubular Rivets: These are like solid rivets but have a small hole in the tail part and therefore, less force is used to form the shop head.
- Blind Rivets (Pop Rivets): They are used in cases where access to the area to be joined is restricted to one side only. A blind rivet is made up of a rivet shank and a mandrel. In this process, the mandrel is pulled and the rivet body on the blind side expands to form the second head and the mandrel is then removed.
Rivets have a high shear load and are ideal for withstanding vibrations. They are used to form permanent joints and are widely used in aircraft structures, bridge construction and in general sheet metal working.
Sheet Metal Screws
Sheet metal screws are screws that are intended to create their own threads in sheet metal when they are inserted in pre-drilled or punched holes.
- Self-Tapping Screws: These have sharper threads and may need a pilot hole to be drilled before the screw is inserted. They form threads by the process of displacement of material.
- Self-Drilling Screws: These have a drill point at the head that drills a hole and creates threads at the same time, thus saving time in assembly.
Sheet metal screws come in different head types (pan, hex, flat) and drive types (Phillips, slotted, Torx). The main benefits are that they are easy and fast to install, using only driving tools and no tapping operation is needed. Their holding power is, however, comparatively lower than self-clinching fasteners and they are more likely to strip if over-tightened especially when used on very thin materials. They are widely applied in HVAC ducting, automotive interiors, refrigerators and other home appliances, and light gauge construction.
Weld Fasteners
Weld fasteners are nuts or studs that are intended to be permanently affixed to a sheet metal part through precise alignment and welding techniques such as resistance welding, projection welding, arc welding, or capacitor discharge (CD) welding. They have specific projections or flange designs that enable the focus of energy in a way that will produce a good weld.
The first advantage is a very strong and permanent fastening for high loads or for applications where different materials have further parts that have to be screwed on. Weld fasteners do not require the creation of holes for the fastener itself (although there may be locating features), which maintains the strength of the sheet.
Disadvantages include the need for specialized welding equipment and experienced operators, heat affecting or marking the sheet metal surface, and the need for the fastener to be compatible with the workpiece. It is widely used in automotive frames and bodies, heavy vehicles and equipment, and industrial machines.
Bolts and Nuts
While often associated with thicker materials, bolts and nuts are also utilized in sheet metal applications, particularly when a high degree of clamping force or the ability to disassemble the joint is required. Typically, this method involves pre-drilling holes in the sheet metal and then securing the components together by tightening the nut onto the bolt. Washers are often used to distribute the load and prevent damage to the sheet metal surface. Various types of bolts (e.g., carriage bolts, hex bolts) and nuts (e.g., standard nuts, lock nuts) are available depending on the specific application requirements.
Threaded Inserts
Threaded inserts are used to create strong, durable and reusable threads on materials that cannot be threaded directly due to their thinness or softness such as sheet metal.
- Rivet Nuts (Nutserts): These are installed from one side like the blind rivet. A tool pulls a threaded mandrel, which causes the insert body to compress and expand against the blind side of the sheet to form a threaded anchor.
- Press-In Inserts: These are similar to self-clinching fasteners that are pressed into holes and may use specific profiles to engage the parent material.
Threaded inserts are very useful when there is a requirement of having strong and reusable threads in thin panels where the access is possible only from one side (for rivet nuts). They are used in automotive industry, aerospace industries, and in the joining of parts to enclosures.
Cage Nuts and Clip-On Nuts
Cage nuts are made up of a nut with a square head and a spring steel cage with two wings or clips. These wings enable the cage nut assembly to be screwed into a square or rectangular aperture in a sheet metal panel, usually a rack rail or enclosure. Clip-on nuts (or U-nuts) work in the same way, being clipped over the edge of a panel or into a rectangular hole to create a threaded hole.
The main benefit of both is that they afford a certain amount of slop or play, so that the holes in the panel do not have to align perfectly with the component being fastened. They also have serviceability, as they can be easily disassembled and replaced in case they are damaged. They are commonly used in IT equipment racks, electrical cabinets, and some automotive applications where devices are mounted on panels.
| Fastener Type | Tensile Strength (N) | Shear Strength (N) | Torque-Out Resistance (Nm) | Vibration Resistance | Typical Applications |
| Self-Clinching Fasteners | 2,000–4,500 | 2,000–4,000 | 5–12 | Excellent (mechanical lock) | Electronic housings, automotive electronics |
| Weld Nuts | 2,500–6,000 | 2,000–5,000 | 10–20 | Excellent (no relative motion) | Automotive frames, heavy-duty assemblies |
| Weld Studs | 2,000–5,000 | 1,800–4,500 | 8–18 | Excellent | Industrial enclosures, machinery structures |
| Solid Rivets | 4,000–10,000+ | 3,500–8,000 | — | Excellent (fully compressed) | Aircraft, bridges, structural components |
| Semi-Tubular Rivets | 2,000–5,000 | 2,000–4,000 | — | Good | Appliance frames, medium-load assemblies |
| Blind Rivets (POP) | 1,000–3,000 | 800–2,500 | — | Moderate | HVAC, lightweight sheet metal structures |
| Self-Tapping Screws | 800–2,000 | 600–1,800 | 2–5 | Poor (loosen over time) | Appliances, light enclosures, budget assemblies |
| Self-Drilling Screws | 1,000–2,500 | 800–2,200 | 3–6 | Fair to moderate (depends on design) | Roofing, siding, construction sheet metal |
| Bolts + Nuts (+ Washers) | 3,000–7,000+ | 2,500–6,000 | 10–25 | Good to excellent (with locking) | Machinery, structural frames, removable joints |
| Rivet Nuts (Nutserts) | 1,800–4,000 | 1,500–3,500 | 4–10 | Moderate | Automotive skins, thin panel threading |
| Press-In Inserts | 2,000–4,000 | 1,800–3,800 | 6–12 | Good | Electronics, sheet metal enclosures |
| Cage Nuts | 1,200–3,000 | 1,000–2,500 | 3–7 | Moderate | Server racks, electronic frames |
| Clip-On Nuts (U-Nuts) | 800–2,000 | 700–1,800 | 2–4 | Poor to fair | Automotive trim, quick panel mounting |
Note: Performance values are typical estimates for medium-carbon steel fasteners in 1.0–2.0 mm sheet metal. Actual performance may vary based on material, installation quality, and design specifics.
Critical Factors for Fastener Selection
Choosing the optimal fastener requires evaluating multiple application-specific factors.
Sheet metal material & thickness
The type and thickness of the sheet metal are the two most important factors that define the choice of the tool. It is important to avoid having dissimilar metals in contact with each other as this will cause galvanic corrosion to occur especially when an electrolyte is present. Fastener material should be of the same type as the sheet metal or at least should be galvanically compatible with the sheet metal. Some of the common sheet metals are aluminum, steel, stainless steel, galvanized steel, copper and brass. They also have different mechanical and corrosion resistance characteristics which determine the type of fastener to be used.
Thickness defines practicality. For example, self-clinching fasteners have minimum thickness requirements for the sheet material. The range of the rivet grip must be equal to the total thickness of the materials to be joined.
Load Requirements
The nature and the amount of loads that the joint must bear are very important. These are tensile, shear, torque, and vibrational forces. Performance data given in fastener datasheets are usually obtained under certain test conditions. The selected fastener must have enough strength margins above the service loads expected to be applied on the structure.
Accessibility for Installation
Determine if both parties have access to the joint or only one of them (blind access). This greatly reduces the number of fasteners available. Blind rivets and some of the threaded inserts are used for blind applications, while self-clinching fasteners, and solid rivets require access from both sides. The type of tooling required and therefore the possible fastener types may also be influenced by the space available around the joint location.
Cost Considerations
Evaluate the total cost, not just the unit price of the fastener. This includes the cost of the fastener itself, any specialized tooling required for installation, the labor time per installation, and potential costs associated with rework or failure. Self-drilling screws might have a higher unit cost but can reduce labor time significantly. Self-clinching fasteners might require investment in press equipment but offer high reliability.
Environmental Factors
The operating environment and environmental conditions influence material and finish selection. Consider exposure to moisture, salt spray, chemicals, temperature extremes, and UV radiation. Stainless steel fasteners or those with appropriate protective coatings (e.g., zinc plating, passivation) may be necessary for corrosive environments. Temperature can affect material strength and compatibility.
Desired Lifespan and Maintenance
Decide whether the joint is to be a permanent one or whether it is to be designed to be dismantled for maintenance or replacement. Rivets and weld fasteners are used to form permanent fasteners. Screws, cage nuts and threaded inserts facilitate disassembly and reassembly but the threads created by the sheet metal screws may weaken with time.
Aesthetic Requirements
In some cases, aesthetics are a concern (such as in consumer electronics, architectural panels), the choice of fastener and type of screw is significant. Some of the factors include whether the fastener head is to be visible or concealed, whether a flush surface on one or both sides is required, the type of head, and the color/finish of the head. Some of the fasteners, such as self-clinching ones or countersunk rivets/screws, provide minimal or even flush head configurations.
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Best Practices for Fastener Installation
Regardless of the specific fastener type, adhering to best practices during installation is crucial for achieving the intended joint performance and avoiding premature failures.
Preparing the Workpiece
Mounting holes should be of the right size and shape and placed in the right position as recommended by the fastener manufacturer. Hole tolerances are often critical. There should be no large burrs that may hinder the proper seating of the holes. The surrounding area of the hole should be free of contaminants such as oil, dirt, and excessive scale that may affect the joint or the next finishing steps. The workpiece should be properly supported during installation to avoid distortion of the workpiece.
Choosing the Right Tools
In most cases, it is recommended that one should use the installation tools that are recommended or recommended by the manufacturer of the fasteners. This includes presses with adequate tonnage and with parallel motion for self-clinching fasteners, the right nose piece and pulling force for blind rivets, right welding equipment and settings for weld fasteners and calibrated torque wrenches or drivers for the screw fasteners. Another factor that leads to installation problems is the use of wrong or damaged tooling.
Proper Installation Techniques
It is important that the installation process is done according to the manufacturer’s instructions to the letter. For press-fit fasteners (self-clinching, inserts), apply force in the axial direction and apply it smoothly until the fastener is fully inserted. Do not “hammer” clinching fasteners. In the case of rivets, it is important to achieve the right upset condition. For screws, turn them in a straight motion and do not apply high speed which may cause heat or stripping of the threads.
Torque Control
In the case of threaded fasteners (screws, bolts, threaded inserts), it is crucial to apply the correct tightening torque. Under-torquing is a condition that results in loose joints and may fail under vibration or load. Excessive tightening can cause thread damage, break the fastener or even damage the sheet metal. Utilize calibrated torque measuring instruments and ensure that the torque is within the recommended values.
Inspection and Quality Check
After installation, visually inspect the fastener for correct seating, flushness (if required), and any signs of damage to the fastener or surrounding material (cracks, deformation). For critical applications, perform sample testing (e.g., push-out or torque tests for clinching fasteners, torque checks for threaded fasteners) to verify installation integrity against specified requirements.
Common Mistakes to Avoid
- Incorrect hole size or tolerance (too large leads to poor retention; too small can damage fastener or sheet).
- Using a fastener not suitable for the sheet material type or hardness.
- Exceeding the fastener’s specified minimum sheet thickness or grip range.
- Applying installation force non-axially (can damage fastener or hole).
- Using excessive installation force or insufficient force/dwell time.
- Improper workpiece support leading to deformation.
- Attempting to install stainless steel clinching fasteners into stainless steel sheets without verifying hardness compatibility (fastener must be harder).
- Over-driving or under-driving screws.
Conclusion
Effective sheet metal fastener selection and installation are critical for product quality, integrating design engineering with manufacturing precision. Understanding fastener types, selection factors, and installation best practices is essential.
However, theoretical knowledge must be complemented by meticulous execution during the fabrication and assembly stages. Adherence to best practices, correct tooling, and rigorous quality control are mandatory. By carefully considering application requirements and leveraging expert fabrication partners where appropriate, engineers and manufacturers can ensure sheet metal assemblies meet performance, cost, and longevity targets. Proper fastening is not merely an assembly step; it is a cornerstone of product quality.
