From consumer electronics to heavy industrial equipment, mechanical fasteners secure components in place, enable assembly and disassembly, and ensure products perform safely and reliably throughout their service life. Understanding the different types of fasteners and their applications is essential to making the right engineering decisions. In this guide, we will introduce what a fastener is, explore the main categories of fasteners, and tell you the key factors to consider when choosing the right fastener for your application.
What Is a Mechanical Fastener?
A mechanical fastener is a hardware device that mechanically joins or affixes two or more objects together. Unlike welding, adhesive bonding, or other permanent joining methods, most fasteners create a connection that can be assembled and disassembled without damaging the parts being joined.
They are typically made from metals such as steel, stainless steel, aluminum, and brass. Plastic and composite fasteners are also common in applications where weight reduction, corrosion resistance, or electrical insulation is a priority. The choice of fastener also varies with the type of connection and the requirements of the application, resulting in a wide range of fastener designs.
Different Types of Fasteners
Fasteners include a wide range of designs, each suited to different connection, load, and assembly requirements. The main types include screws, bolts, nuts, rivets, washers, pins, and inserts.
Screws
Screws are threaded fasteners used to secure components by engaging with a threaded hole or mating component. Depending on the design, screws may use a preformed thread or create one during installation. For example, self-tapping and thread-forming screws can form their own mating threads, while standard screws typically require a pre-tapped hole or threaded nut. They are widely used in furniture, enclosures, circuit boards, and automotive components.
Typical types and applications of screws include:
- Sheet metal screws: Sharp, self-threading screws that can bite into sheet metal, wood, and plastic without a pre-tapped hole.
- Machine screws: Designed for pre-drilled holes, with fine, precise threads suited for machine components and precision assemblies.
- Hex Lag screws: Long, coated screws with coarse threading running most of the shaft, typically used for heavy-duty woodworking and structural connections.
- Wood screws: Sharp-pointed screws with widely spaced threads, designed to grip fibrous wood without splitting it.
- Cap screws: They have a larger head and are commonly used to assemble machinery housings and appliances.
Bolts
These fasteners are designed to pass through pre-drilled, unthreaded holes and are secured on the opposite side with a mating nut. This combination can create strong, detachable joints and can provide reliable clamping in high-load and high-vibration applications. They are widely used in structural steel connections, machinery frames, and automotive assemblies.
Typical types and applications of bolts include:
- Hex bolt: It features a hexagonal head designed for tightening with a wrench or socket tool and is suitable for general-purpose construction and machinery assembly.
- Carriage bolts: For wood-to-metal connections where a smooth, tamper-resistant head is needed.
- Double-end bolts: They have sharp threads on both sides, used for the joining of two flanges together.
- U-bolts: Bent into a U shape with threading on both straight ends, these fasteners wrap around cylindrical items such as pipes or conduit.
- Eye bolts: Fitted with a circular loop in place of a standard head, these bolts provide an anchor point for ropes, chains, or cables to pass through or attach to.
Nuts
These internally threaded fasteners pair with bolts or screws to clamp components together. Some are engineered specifically to resist backing off under repeated stress, while others prioritize quick, tool-free access. They are a staple across automotive, industrial machinery, and general assembly work.
Typical types and applications of nuts include:
- Hex nuts: Suitable for general-purpose fastening with standard bolts.
- Lock nuts: For applications exposed to vibration where loosening must be prevented.
- Wing nuts: For connections that need to be hand-tightened or loosened without tools.
- Acorn nuts: They feature a rounded top that encloses and protects the exposed end of a bolt.
- Weld nuts: Designed to be welded onto metal surfaces.
Rivets
These permanent mechanical fasteners consist of a smooth cylindrical shaft with a head on one end. After installation is complete, the opposite end is deformed, typically by hammering or pulling with a rivet gun, to form a second head that clamps the joined materials together. The resulting permanent joint provides reliable resistance to loosening under vibration and repeated loading. Rivets are widely used in aerospace, sheet metal fabrication, and structural applications.
Typical types and applications of rivets include:
- Solid rivets: Consisting of just a shaft and head, suitable for high-strength structural and aerospace applications.
- Blind (pop) rivets: These hollow fasteners use an internal mandrel that snaps off once pulled through, used for joints accessible from only one side.
- Tubular rivets: They are similar to solid rivets but feature a partial hole at the tail end, used for lighter-duty sheet metal and consumer product assembly.
Washers
These flat, typically disc-shaped components are placed under a fastener’s head or nut. Washers help spread clamping force over a wider surface area, protect finished surfaces from damage, and reduce friction during tightening. They are a small but critical part of nearly every threaded assembly.
Typical types and applications of washers include:
- Flat washers: Suitable for distributing load and protecting surfaces under a fastener head
- Lock washers: For applications exposed to vibration where loosening must be resisted
- Spring washers: Absorb shocks and compensate for slight loosening, used in electrical connections and automotive suspensions.
Pins
These simple cylindrical or tapered fasteners are used to align, locate, or lightly secure components rather than carry heavy structural loads. Pins are a low-cost way to maintain accurate positioning between mating parts during assembly and operation. They are frequently used in machinery, tooling, and fixtures.
Inserts
These fasteners create a secure attachment point in materials that can’t be threaded directly, such as drywall, concrete, or thin-walled plastic components. For example, threaded inserts are commonly molded or pressed into plastic parts to provide a durable, reusable metal thread. Inserts are common across construction, electronics, and injection-molded assemblies.
How to Choose the Right Fastener for Your Application
Selecting the right fastener requires balancing mechanical performance, material compatibility, and manufacturing practicality. Here are the key factors to evaluate:
Load and Stress Requirements
The fastener should be selected based on the tensile, shear, and vibration loads it will experience. High-stress structural applications typically need bolts and studs, while lighter assemblies may only need screws.
Material Compatibility
Fastener material should be selected based on the materials being joined and the operating environment. Carbon steel suits general applications, stainless steel works well in corrosive or outdoor environments, and aluminum is preferred where low weight is important. When joining dissimilar metals, check material compatibility to minimize galvanic corrosion.
Environmental Exposure
The operating environment can affect fastener performance, especially when components are exposed to moisture, chemicals, or extreme temperatures. Such applications may require corrosion-resistant coatings or materials such as stainless steel and specialty alloys.
Assembly and Disassembly Needs
If a product will require future maintenance or part replacement, threaded fasteners are typically preferable because they can be removed and reused. For permanent, high-strength joints where disassembly is not required, rivets can provide a secure connection with consistent clamping between the joined materials.
Manufacturing Method
The manufacturing process and part design can influence the choice of fastener and how it is integrated into the assembly. For injection-molded plastic components, threaded inserts, snap-fits, or self-tapping screws are common solutions that integrate well with molded parts. A DFM review can help determine the most suitable fastening method before tooling begins.
Cost and Volume
For high-volume production, fastener cost can have a significant impact on total assembly cost. Where practical, standardizing fastener types across a product line can simplify sourcing and inventory management while making assembly more consistent.
Fastener Installation Best Practices
Fastener installation directly affects the strength and reliability of the finished joint. Following a few core practices helps ensure joints perform as intended and reduces the risk of costly rework or field failures.
- Use the correct torque: Over-tightening can damage threads or cause fatigue failure, while under-tightening can reduce the joint’s resistance to loosening under load. Applying the recommended torque values, ideally with a calibrated torque wrench, keeps clamping force within the intended range.
- Match the fastener to the hole and thread specification: The wrong drill or tap size can result in a weak or stripped connection. Confirming hole diameter, thread pitch, and depth before installation can avoid these issues.
- Use thread lockers or lock washers where vibration is a concern: For assemblies exposed to dynamic loads, a thread-locking compound or lock washer helps maintain clamping force and prevents fasteners from backing out over time.
- Follow a consistent tightening sequence on multi-fastener joints: A star or crisscross pattern distributes clamping force evenly and reduces warping.
- Inspect fasteners before reuse: Threads that are damaged, corroded, or deformed should be replaced rather than reused, especially in structural or safety-critical applications.
Conclusion
Mechanical fasteners include many forms, from screws and bolts to rivets, washers, pins, and inserts, with each type serving a different role in an assembly. Choosing between them depends on how the joint needs to function. Understanding these differences makes it easier to select a fastener that suits both the application and the way the product will be assembled and maintained.
For new product designs, our DFM review can help you evaluate the proposed fastening approach before production. No matter what your application is, you can trust our manufacturing service to provide you with fasteners that will meet your standards. Contact us for a quote now!
