Automotive engineering is about fine details and accuracy, with many automotive parts working together to ensure the car performs well, is safe, and is reliable. Automotive fasteners are often not given much attention, but they are still very important structural components.
It is important for engineers, manufacturers, and all others involved in the automotive industry to know about the different types of automotive fasteners, materials, and their uses. The automotive design process places significant emphasis on selecting the right material and the right fastener for each application.
What Are Automotive Fasteners and Why Do They Matter?
Automotive fasteners are mechanical devices that join or secure two or more small parts of a vehicle. Their function is much more than joining vehicle components; they are critical to the vehicle’s structural strength, safety while functioning, and its durability over time. Every fastening device is chosen based on the specific conditions it will be subjected to and its purpose, aiming for straightforward solutions where possible.
Automotive fasteners perform critical functions in the automotive part manufacturing industry that cannot be overlooked. The failure of a single fastener, in certain situations, can result in annoying things like rattling noises and component misalignment, or serious issues that can lead to system failures that put the vehicle’s safety at risk. Exposed to constant vibrations, temperatures and corrosive forces, the environment within a vehicle is incredibly stressful. This is why different fasteners, such as plastic automotive fasteners and metal ones are need to be reliable and strong, as well as specially tailored for their designated purpose. The design and application of fasteners undergo extensive consideration in the manufacturing and maintenance of automobiles. Continuous innovation in vehicle technologies like light weighting and the increase in electric vehicle adoption trends provide additional focus towards material science and fastener design.
Common Types of Automotive Fasteners
The assortment of fasteners used in the car industry is wide, as every one of them is made for a specific mechanical need, servicing, processes of assembly, and service conditions. Below are some of the most common automotive fasteners.
Bolts
In all of automotive uses, bolts rank as one of the most widely used and important mechanical fasteners. A bolt is mostly defined by a head on one end and an externally threaded shank. It is designed to be inserted through non-threaded holes in assembled parts and is usually tightened or released by torquing a mating nut or a threaded hole in one of the components.
Numerous variations, such as:
- Hex head bolts: the most common, offering good torque application.
- Carriage bolts: with a smooth, domed head and a square neck to prevent turning.
- Flange bolts: have a washer incorporated with the bolt directly under the bolt’s head for purposes of load distribution. Hex flange bolts are a popular option.
- U-bolts: look like the letter U, with threads on both arms, commonly employed for holding together pipes or components of suspension components.
All sorts of bolts are crucial for the engine assemblies, supporting structures like the chassis frames, the suspension systems as well as the wheel hubs like the axle bearing.
Screws
Screws are bolts-like fasteners with external threads, but they are usually meant to be put into a hole already threaded or to bite their internal thread into softer material (self-tapping screws) as they rotate downwards. Unlike bolts, screws, including the common hex screw and machine screws, are usually tightened to the rotating head without the direct use of a nut on the other side of the assembly. Automotive screws include:
Screws are extensively used to tighten interior panels and the electronic modules of cars as body trims and dashboards. Examples include the pan head screw and the countersunk head screw.
Nuts
Nuts, including automotive nuts, are designed to fasten with a bolt’s external thread and thus, they are internally threaded. They are important for forming clamped joints as they provide the needed clamp pressure when screwing. The common shape of nuts is a hexagon because they are designed to be tightened with a wrench. Common types include:
- Hex nuts: standard general purpose.
- Lock nuts: nylon insert lock nuts or distorted thread lock nuts, specially crafted to prevent loosening when vibration is applied.
- Cap nuts: also known as acorn nuts, are used to cover the end of the bolt and for protection with a domed top.
- Flange nuts: incorporating an attached washer.
- Castle nuts: slotted so that a cotter pin can be used to prevent loosening.
Nuts are ubiquitous, used in conjunction with bolts across nearly all vehicle systems, , forming a secure connection.
Rivets
Rivets are a type of fastener that can withstand high amounts of stress. Before installation, a rivet is a smooth cylindrical shaft with a head on one end. Once a rivet is placed through its designated hole, the tail end is deformed to create a new head and securely hold the different parts together. Automotive rivets include:
- Solid rivets: They must be placed from both sides of the sheet metal.
- Blind rivets: Otherwise known as pop rivets, these can be put in from one side and are commonly used with body panels and trim.
- Tubular rivets: These have hollow ends which makes clinching them easier.
They are best regarded because of their strength, ability to withstand vibration, and ability to join different materials together. Rivets are often used in the chassis of a vehicle, the body structure, and also used for nameplates or other trim pieces.
Washers
A washer is a disk-shaped plate with a central hole that usually accompanies bolts, nuts, or any other threaded joining tool. Their function includes evenly distributing the load caused by the fastening device, preventing any damage to the joined parts by offering a smooth surface, and acting, when needed, as a spacer, spring, or locking mechanism. They serve distinct functions: plain washers distribute weight, while spring washers add flexibility to combat loss from vibration. Additionally, washers come in different shapes and styles, showcasing their versatility. Due to their versatility, washers can be found in practically every vehicle’s bolted or screwed connections.
Clips
Clips represent a heterogeneous set of fasteners, primarily made of plastic or metal, intended to retain pieces together or in a set position without using threads. As there are no threads, they make use of either spring properties or features that lock into place in order to remove inter-component motion. Types of automotive clips include:
- Trim clips: used to attach both internal and external trim panels.
- Wire harness clips: dedicated to holding electrical wiring.
- Hose clips: Clamps that are often put in this category.
- Panel clips: designated for parts of body panels.
They serve parts that require maintenance or servicing frequently, as they can be quickly disassembled and reassembled around the vehicle.
Clamps
Clamps are tools made specifically for holding or securing items firmly to restrict movement or separation through the application of inward pressure. In an automotive context, they are important for fluid and air systems. Clamps are best known as hose clamps, which seal the ends of hoses to fittings located in cooling systems, fuel systems, and air intake systems. Other prevalent types include worm gear clamps, spring band clamps, and ear clamps, which vary in the manner of tensioning, sealing, and their overall design.
Pins
These are pins that are fasteners, either cylindrical or tapered, that perform locating, aligning, or joining tasks. In some cases, a rotational or pivoting function may be permitted, while in other instances the connection may be rigid and resistant to shearing forces. In the automotive industry, we may include:
- Dowel pins: for securing two parts together, such as halves of an engine block.
- Cotter pins: split pins which are placed inside a bolt hole and secured with a castle nut to retain their rotational motion.
- Clevis pins: Used with a cotter pin for spanning pivot joints in shafts.
- Spring pins: rolled or coiled pins that are fitted into a hole and apply outward radial force.
They are critical in linkages, transmissions, and securing rotating components.
Studs
Studs are a type of fastener that is externally threaded. They bear a resemblance to bolts, they can also be understood as threaded rods. One side of the stud is designed to be inserted in a component for permanent installation (such as being screwed into a tapped hole, welded, or pressed in). This leaves the other end threaded to allow a nut to be attached. A good example would be wheel studs, which are pressed into the wheel hub and used for attaching wheels with lug nuts. Another important example are the engine cylinder head studs, which screw into the engine block and allow the cylinder head to be secured down with nuts. As opposed to other types of fasteners, like bolts, studs are more beneficial where there is repeated assembly and disassembly due to their minimal wear on the threaded holes.
Springs
Springs in particular are not perceived as primary fasteners the way bolts or screws are, however, they do perform a fastening or retaining function by extending a constant force. For instance, an engine valve spring will hold valves closed and springs used in other various devices will maintain pressure and keep components secured. Furthermore, coil and leaf springs play a crucial role in a car’s suspension system. They act as a fundamental to suspension systems, effectively fastening the axle assembly to the vehicle chassis and allowing for movement at the same time.
Specialty Fasteners
Aside from the common types, there is a specialized fastener type which are usually created for particular automotive uses or to satisfy certain production needs. These include:
- Quick-release fasteners: for panels requiring frequent removal.
- Self-clinching fasteners: PEM® nuts, studs, standoffs that masterly bond to sheet metal parts.
- Additionally, automotive manufacturers come up with custom designs such as thread forming screws for specific materials.
- Such devices are usually invented to make assembly quicker, decrease overall weight, or improve performance for specialized uses.
For quick reference, the table below contains a summary of the fastener types discussed above that are categorized by their uses and advantages in automotive applications:
| Fastener Type | Description | Typical Use Cases | Key Advantages |
| Bolts | Threaded fasteners used with nuts or tapped holes | Engine blocks, suspensions, chassis frames | High strength, reusable |
| Screws | Threaded fasteners often self-tapping or for pre-threaded holes | Interior panels, trim, electronics | Versatile, good for plastic/metal |
| Nuts | Internally threaded, used with bolts/studs | All structural and serviceable joints | Provides clamp force |
| Rivets | Permanent fasteners with deformed tails | Body panels, structural joins | Vibration-resistant, good for dissimilar materials |
| Washers | Discs used with bolts/screws to distribute load | Nearly all bolted joints | Load distribution, vibration damping |
| Clips | Snap-fit or spring fasteners, often plastic | Trim, wiring, panels | Quick installation/removal |
| Clamps | Devices that apply pressure to hold parts | Hoses, air/fuel systems | Ensures tight seals |
| Pins | Cylindrical or tapered fasteners for alignment or shear resistance | Transmissions, linkages, brake components | Alignment and shear load handling |
| Studs | Threaded rods fixed at one end, used with nuts | Engine heads, wheel hubs | Prevent thread wear in base material |
| Springs | Elastic fasteners that apply preload or retain parts | Valve trains, suspension | Constant force, damping |
| Specialty Fasteners | Custom designs for niche needs | Racing, electronics, trim | Lightweight, fast assembly, proprietary features |
Common Materials Used in Automotive Fasteners
The selection of the material for an automotive fastener plays a huge role and is influenced by several factors such as strength, surface area, area of application, corrosion resistance, operating temperature, weight, synergism with other materials used, and total cost, particularly in relation to engine parts. Below is the most common material used in automotive fasteners:
Steel
Steel, in its alloyed forms, is the most widely used material for automotive fasteners due to its strength-to-cost ratio and versatility to be worked on and shaped. Rust protection is often applied through coatings.
- Low-carbon steel: Used for less important applications like some screws, clips, light duty bolts and other components that do not require strngth.
- Medium-carbon Steel: Subjected to some form of heat treatment (quenched and tempered) for greater tensile strengths (e.g., SAE Grades 5 and 8, or ISO Classes 8.8, 10.9, 12.9). These fasteners serve major structural functions in engines, drivetrains, suspensions, and chassis.
- Alloy steels: Components such as chromium, molybdenum, and nickel are added to improve certain features like chromium, toughening and high temperature strength. Used for extremely high-strength bolts and studs in demanding applications.
Steel fasteners are commonly coated (eg with zinc, phosphate, or proprietary coatings) to improve corrosion resistance.
Aluminum
Applications of Aluminum fasteners are increasing within the automotive industry, particularly in areas such as body panels and constituent parts of the engine as well as the interiors due to the objective of weight reduction. Aluminum provides adequate resistance to corrosion in a range of environments, while also possessing a favorable strength-to-weight ratio. With these advantages, aluminum exhibits difficulty when competing with steel since it possesses lower strength and a greater thermal coefficient of expansion. Special attention should be paid to dielectric design when aluminum fasteners are used with other metals, specifically steel, due to galvanic corrosion.
Plastics
Different types of engineering plastics, including nylon, polypropylene, and acetal, are utilized for various plastic fasteners most particularly for clips, retainers, and light array of push-in fasteners along with screws. As compared to metals, plastics are very lightweight, immune to corrosion, electrically insulating, good dampers, and can be shaped into different molds for effortless snap-fit assembly. However, the strength provided by plastics is considerably less than metals limiting their applications for trim, and interior components at low-load settings.
Titanium
Titanium alloys are exceptional materials for fasteners, offering an unrivaled strength-to-weight ratio (stronger than several steels yet 40% lighter) and unparalleled resistance to corrosion, even at high temperatures.) However, titanium costs significantly more than steel or aluminum. Its application in mass production vehicles is mostly restricted to high-performance, racing, or extreme weight reduction situations such as exhaust systems, suspension parts, and engine valve train components for some exotic cars where cost considerations are secondary.
Brass
Brass, an alloy containing copper and zinc, is employed for automotive fasteners in limited applications where good conductivity, resistance to corrosion (especially fuel and some chemicals), and non-magnetic characteristics are needed. While it is weaker than steel, it has its purpose. Brass screws, nuts and fucking terminals can be used within electrical systems and in some fuel system components. Its bright color can be appealing for some non-functional use, but it is uncommon in modern automotive design.
Tips for Choosing the Ideal Automotive Fastener
Fastener selection is critical to ensuring the safety, dependability, and durability of an automotive assembly. Several factors must be looked into, including the coefficient of friction along with load requirements.
Load Requirements
The type and magnitude of the loads on the fastener are critical first focus areas. It includes tensile (pulling apart), shear (sliding), torsional (twisting) and even dynamic loads from impact and vibration. Additionally, the fastener’s material, diameter, and the amount of thread engagement must possess sufficient strength to tackle these loads along with appropriate safety factors.
Working Environment
Faster choice is influenced greatly by the operational environment. These include:
- Temperature: Exceeding ranges (such as those found in exhaust systems and engine components) can weaken a fastener’s strength and cause it to loosen due to overheating and cooling. Such regions require materials with the right level of thermal stability.
- Corrosion: Road salt, chemicals, and moist conditions subject fasteners to corrosion. Corrosion-resistant materials such as aluminum, stainless steel or even plastic as well as protective coating on steel fasteners are required.
- Vibration: Vehicles are under constant vibration which subjects fasteners to slow loosening. Special anti-loosening features as well as particular designs of the fastener are essential.
Material of Joined Parts & Fastener Compatibility
The components to be joined are equally important in choosing the fastener.
- Galvanic Corrosion: If moisture is present, joining different metals with a fastener can result in galvanic corrosion. The fastener used is also recommended to be galvanically isolative or compatible.
- Material Strength: Before the proper clamping load is achieved, a fastener should not be too weak so that it fails, nor too strong that it damages softer joined materials when they are tightened.
- Thermal Expansion: Special consideration must be given for parts that undergo large temperature differences due to the presence of different expansion coefficients in relation to the fastener and joined pieces, especially in thermal ranges with considerable temperature oscillations.
Cost
Cost will always be a component in mass production, while performance and reliability remain critical. The selected fastener must fulfill all engineering expectations, but at a better value. This is usually a balance between the expense of the material, the complexity of manufacturing the fastener, and assembling it. The application of exotic materials or highly specialized designs is usually reserved for when standard options are insufficient.
How to Prevent Automotive Fasteners from Loosening？
In automotive engineering, vibration, thermal cycles, and other dynamic loads are some of the major causes of loosening of fasteners, which is of great concern due to potential repair costs. Here are several strategies to prevent this:
Application of Locking Devices
Various mechanical locking features can be incorporated:
- Lock Nuts: Nylon-insert lock nuts and all-metal prevailing torque nuts (i.e., distorted thread or elliptical offset nuts) resist rotation by means of the friction they create on the bolt threads.
- Lock Washers: Spring washers (helical or conical/Belleville) place load on the joint. Toothed lock washers (star washers) embed themselves into the fasteners and the joint surfaces.
- Thread Locking Adhesives: Anaerobic adhesives in liquid form are applied to the honed threads. They cure in the absence of air by locking the threads and sealing against corrosion.
- Serrated Flange Bolts/Nuts: The serrations embed themselves in the adjoining surface to arrest loosening of bolts.
Material Selection and Vibration Resistance
The intrinsic elasticity of the fastener and joint materials can help retain preload. Choosing materials with appropriate fatigue resistance is also equally critical. Some of the designs of fasteners are more resistant to vibration loosening than others. The total stiffness of the joint, created by the fasteners and the components being clamped, is also a factor.
Proper Torque Application and Torque Wrenches
To prevent loosening, correct preload (clamp force) achieved with the specified tightening torque, which represents the rotational force applied, is the most basic method.
- Torque Specifications: Each joint has a specific torque value set by the engineers. Insufficient tightening will lead to slack in clamp load, while excessive tightening will damage threads or yield the fastener.
- Torque Wrenches: Click, beam and digital wrenches are calibrated torque tools that must be held while mechanically controlled during assembly and maintenance. They are set to apply the required specific torque. For critical joints, torque-angle tightening aims for even better precision.
Regular Inspection and Maintenance Schedules
For some critical fasteners, specifically in heavy vehicles or high-performance ones, regular check-ups and torque checks (if specified by the manufacturer) are part of the maintenance schedule. Visual inspection can identify externally observable signs of corrosion or fatigue that would cause loosening or failure.
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FAQS
What are three types of automotive fasteners?
Bolts, screws, and rivets are three common automotive fasteners used to assemble and secure automotive components.
How many fasteners does a car have?
Most cars contain between 3,000 and 5,000 fasteners, depending on the vehicle’s complexity.
Are automotive fasteners reusable?
Some metal fasteners, like standard bolts and nuts, can be reused if undamaged. However, torque-to-yield bolts, locking nuts, and many plastic clips are designed for one-time use and should be replaced to ensure safety and reliability.
