The nut is a mechanically designed part that works in conjunction with bolts and screws to form joints in vehicle manufacturing and industrial applications. The nut is very small in size, yet it directly controls the clamping power of joints.
CNXD Auto is an automotive and industrial fastener supplier based in Wenzhou, China. We produce nuts that conform to the standard as well as custom-made nuts.
This guide focuses on the different types of automotive nuts, highlighting their important characteristics, specifications, and applications. The purpose of this guide is to assist engineers, buyers, and distributors in selecting the correct fasteners.
Nut Basics: How a Nut Works with a Bolt
A nut is defined by five primary parameters, which are standardized under DIN, ISO, ASME, and SAE specifications depending on the market.
The parameters are:
- Thread specification – metric per ISO 68-1 or unified inch per ASME B1.1
- Across flat (AF) size
- Height or thickness
- Material grade
- Surface finish
A nut must match the mating bolt or screw in thread size, pitch, and strength class. According to ISO 898-2, metric fasteners such as nuts must have property classes such as Class 8 or Class 10. These should match the same bolt class to ensure a certain clamp load. The mismatch of strength grades will lead to potential failure of the weaker part.
In automotive and industrial service environments, vibration, thermal cycling, and dynamic loading are the main factors that cause joint loosening. Nut conditions must be based on these factors rather than on thread size.
The following sections cover the different types of automotive nuts, their designs, and applications. You can also download the Automotive Fasteners PDF guide for more information.
General-Purpose Nut Types
- High-strength serrated nuts in SS304/316. Ideal for heavy industry and mining, offering superior corrosion resistance and structural stability.
The term general-purpose nuts typically refers to common nuts for all purposes in regular assembly, repairs, and construction.
Hex Nuts: The Standard Structural Nut
The installation of the hex nut is simple due to the nature of the tools needed for its fastening. This kind of nut goes with a variety of bolts and studs. Hex nuts can be found in machine assemblies and automotive frames.
A hex nut has six sides and is mainly used in general mechanical and structural connections. The six-flat geometry allows installation and removal with standard open-end, box, or socket wrenches.
The nuts conform to ISO 4032 (metric regular), ISO 4033 (metric tall/high), DIN 934, or ASME B18.2.2 (inch series).
Hex nuts are available in a range of metric and inch sizes. Metric nuts are commonly specified by property classes such as 5, 6, 8, 9, 10, and 12. Inch-series nuts are common in SAE J995 Grades 2, 5, and 8.
Flange Nuts: For Integrated Load Distribution
A flange nut is a hex nut with an integral circular flange on the bearing face. It is commonly used in automotive chassis brackets, engine accessory mounts, stamped parts, and HVAC panel assemblies.
Flange nuts outperform standard hex nuts by increasing the load-bearing surface area. This design distributes clamping force more widely to prevent surface damage or pull-through on thin and soft materials.
The serrated flange nuts (DIN 6923) have teeth under their surfaces that engage with the mating surfaces to prevent any loosening. The serrated nuts do not require any lockable components, whereas non-serrated nuts distribute loads without leaving any marks on the surfaces.
Round Nuts: Compact Profile for Shaft Applications
Round nuts, or bearing lock nuts, feature a cylindrical outer profile with slots or spanner holes. You can install them using specialized spanners or hook wrenches. Common standards include DIN 981 (slotted hex bearing lock nut) and ISO 2982-1.
The compact, circular profile fits into tight spaces where standard hex nuts cannot. Use a pin spanner or hook wrench in the slots to apply precise torque. These nuts secure shaft ends, adjust bearing preloads, and position mechanical components.
- This DIN 981 slotted hexagon bearing lock nut is manufactured from high-strength carbon steel or stainless steel, offering multiple surface treatments including black oxide, zinc plating, and nickel plating to meet diverse operational requirements for corrosion resistance and wear resistance.
What are Locking and Welded Nut Solutions?
- This DIN6926 stainless steel flanged nylon lock nut is forged from high-grade SS304/SS316 stainless steel, offering exceptional anti-loosening performance and corrosion resistance.
Locking nut solutions are included in the types of automotive fasteners. These fasteners are designed to resist loosening from vibration, rotation, or cyclic load.
On the other hand, welded nut solutions are nuts that are permanently attached to a metal part by welding. This design creates a fixed threaded attachment point.
Locking Nuts: For Vibration-Prone Environments
Types of automotive fasteners exposed to constant vibration need a positive locking mechanism. While regular hex nuts cannot retain their grip during cyclic loading, locking nuts can retain theirs due to some mechanical characteristics.
Locking nuts are common in vehicle suspension joints, chassis fastening, exhaust mounts, and high-vibration industrial equipment.
Common locking nut designs include:
- Nylon insert lock nuts: These components use ISO 7042 / DIN 985 prevailing torque nuts. A nylon ring deforms around the bolt threads to create a secure lock. Since the nylon does not recover after removal, treat these as single-use fasteners.
- All-metal prevailing torque nuts (per ISO 7042, DIN 980): The metal nut body is deformed or elliptical at the top section, which creates thread interference. This design is suitable for temperatures above the service limit of nylon (approximately 120°C).
- Serrated flange lock nuts (per DIN 6923): The flange serrations engage the mating surface and resist rotation. The serrations are a secondary locking feature supplementing thread friction.
Weld Nuts: For Creating Permanent Threaded Points
Weld nuts allow you to resistance-weld or projection-weld them directly to steel plates before assembly. These nuts create permanent, flush threads so you can bolt parts together without accessing the back of the panel.
Common weld nut designs include square (DIN 928), hexagonal (DIN 929), and round projection types (DIN 6916). On sheet metal, four-claw weld nuts (DIN 928A) use prongs to grip the surface. The projection geometry concentrates the weld current to ensure consistent fusion depth.
Weld nuts are commonly used in automotive applications, such as body-in-white (BIW) assembly, seat frames, door frames, firewall brackets, and structural closures.
- This 304 stainless steel square stud with four-jaw weld-on flange (DIN 928A Type B) is manufactured from high-strength A2-70 grade material, offering excellent corrosion resistance and weldability.
Special Function Nuts for Assembly and Service
- This DIN 7985 Stainless Steel Hex Socket Cap Head Screw is engineered for applications requiring precision, durability, and corrosion resistance.
Special function nuts simplify installation, maintenance, and replacement in specific applications. These are designed for non-standard, purpose-built nuts to solve unique assembly and service challenges.
These nuts replace standard hex nuts when you need faster installation, better retention, or easier maintenance. They boost assembly productivity and cut downtime during repairs.
Cap Nuts: For Thread Protection and Exposed Joint Finishing
Cap nuts feature a closed dome that covers and seals the exposed bolt end. They are also called acorn nuts or dome nuts. The closed end prevents contact between the thread end and the environment, reducing corrosion ingress and mechanical damage.
Cap nuts are commonly used in automotive exterior fasteners, railing systems, and outdoor furniture. They are ideal where thread protection or finished appearance is a requirement.
They are specified per DIN 1587 (metric, low form), DIN 986 (metric, with self-locking insert), and ASME B18.6.3 (inch series). Material options include carbon steel, stainless steel A2-70 and A4-80, and brass for decorative applications.
Castle Nuts: For Mechanically Secured Joints
Castle nuts (also called slot nuts) have slots that are equally spaced on the upper surface. The securing process involves tightening the nut, followed by the insertion of the cotter pin through the hole of the bolt and the slots of the nut. This is done to create a locking effect, which prevents the nut from turning.
Unlike other locking nuts, you can easily inspect the pin during maintenance to ensure everything stays safe. These are manufactured to comply with DIN 935, ISO 7035, and ASME B18.2.2 standards using high-strength carbon or stainless steel. Use castle nuts for steering linkages, wheel hubs, and axles, or anywhere you cannot afford a fastener failure.
- This DIN935 Stainless Steel Slotted Hexagon Nut is manufactured from high-quality A2-70 stainless steel, offering excellent strength, corrosion resistance, and reliability for demanding industrial applications.
Wing Nuts: For Tool-Free Access
Wing nuts feature two flat “wings” so you can tighten or remove them by hand. They work perfectly for parts you need to adjust or service frequently without reaching for a wrench.
These wing nuts conform to the DIN 315 and ASME B18.17 specifications. As you manually tighten them, do not apply them to structural joints since they bear little weight. Instead, use them on access doors and display frames where they undergo frequent adjustments.
- This stainless steel butterfly nut is manufactured from high-grade 304/316 stainless steel or multi-grade alloy steel, suitable for industrial applications demanding high connection and fastening requirements.
Sheet Metal and Blind Fastening Nuts
Thin sheet metal and hollow sections create a unique challenge: they can’t handle standard nut loads. You can only access one side.
The following types of automotive fasteners solve these problems without requiring you to tap threads or access the back of the panel.
Rivet Nuts: Blind Threaded Inserts
- This aluminium knurled closed rivet nut is manufactured from high-strength aluminium alloy, suitable for securing sheet metal and structural components where tapping is impractical.
Threaded nuts, or rivet nuts, allow you to provide a strong thread on a piece where you can only work from one side. Place the nut into the prepared hole. Tighten it with a setting tool until the shank collapses and locks against the back of the panel.
Choose between open-end styles for standard bolts or closed-end versions to block out fluids and dirt. These are available in carbon steel, aluminum, and stainless steel with smooth, knurled, or hexagonal bodies to prevent the nut from spinning.
Use them for door panels, aluminum extrusions, and appliance housings, or any hollow or closed section where traditional nuts won’t work.
Press Nuts: Press-In Fasteners for Sheet Metal
Press nuts or self-clinching nuts provide permanent high-strength threads through direct pressing into a previously punched hole. Using a hydraulic press, the nut’s shank pushes the metal into the undercut groove. This creates a secure joint that will not pull or twist away.
These nuts work on sheets as thin as 0.9 mm and leave a perfectly flush finish on one side. This flat profile makes it easy to stack panels or use automated assembly lines. They are common in car subassemblies, server racks, and electronics, or anywhere you need precision threads in thin metal.
- This self-clinching rivet nut is manufactured from high-strength carbon steel and SS304/SS316 stainless steel.
U Nuts: Clip-On Panel Edge Fasteners
U-nuts (or clip nuts) are U-shaped spring steel fasteners that simply slide over a panel edge or into a slot. Spring force ensures that they remain fixed automatically; thus, no need to hold the nut while installing the screw. Therefore, they are ideal for fast assembly processes in high-volume production.
The design does away with the need to tap threads before installation because the screw creates its thread by itself on the nut body. The spring steel is flexible to accommodate vibrations as well as varying panel thicknesses (0.6 mm to 3.0 mm). They are used in car interiors, dashboard panels, and HVAC systems.
- This A2-70 stainless steel U-bolt is manufactured from premium SS304 material, offering exceptional corrosion resistance and structural stability.
T Nuts: Embedded Fasteners for Wood and Composite Materials
The T-nut, also called the Tee Nut, has a flanged head that is sharp at the end, which digs into the wood. Drive it by pressing or hammering the nut to the underside of wood, plywood, or composites. This keeps the nut steady without spinning.
Once installed, the T-nut provides a durable steel thread in materials that normally can’t hold a bolt. To install one, simply drill a hole for the barrel and seat the flange flush against the back surface. They work best for seating, wooden frames, and any architectural woodwork that you need to bolt and unbolt frequently.
Custom and Other Nut Options
There are times when customers require customization for projects. In these cases, we ask them to provide a drawing of the types of nuts with pictures for more tailored-fit options.
Custom Nuts or Application-Specific Designs
Sometimes, a standard catalog nut simply isn’t enough. Custom nuts are manufactured based on specific drawings and requirements. The designs incorporate non-standard threads, unique dimensions, or integrated locking features.
OEM customers often request custom solutions like:
- Specialized Materials: High-strength grades like alloy steel 10B38 or Grade L9.
- Extreme Durability: Salt spray resistance exceeding 500 hours (ISO 9227).
- Precision Engineering: Controlled hardness ranges and specific thread tolerances (ISO 965).
Other Nut Types or Niche Designs
The “Other Nuts” category includes specialty designs for specific mechanical systems that fall outside of common nut families. These include:
- Square Nuts: Provide a larger surface contact area for better wrenching.
- Coupling Nuts: Also known as extension nuts, these connect two threaded rods or studs.
- Pipe Union Nuts: Used specifically for joining sections of piping.
- Slotted Round Nuts: Designed for use with specialized spanners in circular assemblies.
If you can’t find the specific part you need in our main catalog, you can also check the automotive Fasteners pdf guide for more information.
How to Choose the Right Nut for Your Application
Choosing the right types of automotive nuts requires balancing several technical factors at once. Use this guide to ensure your fastener selection matches your project’s needs:
- Thread and Strength Matching: Always match the thread size, pitch, and tolerance class between the nut and bolt. Ensure the nut’s strength grade meets or exceeds the bolt’s grade to prevent stripping.
- Material Thickness and Access: For thin or soft materials where you can only reach one side, skip the standard hex nuts. Instead, use rivet nuts, press nuts, or T-nuts designed for “blind” installation.
- Vibration and Movement: Standard hex nuts can vibrate loose over time. Choose locking nuts, weld nuts, or castle nuts for chassis, suspension, or exhaust parts to ensure the joint stays secure under constant motion.
- Corrosion Resistance: Use stainless steel for marine or food-contact environments. Choose zinc-nickel-coated carbon steel for underbody parts that need to survive salt and moisture.
- Tooling and Installation: Weld nuts need welding equipment, while rivet nuts and press nuts require specialized pull tools or presses. For a tool-free setup, U-nuts and T-nuts are great options as long as they fit your panel thickness.
Examples of Applications:
- Automotive body sheet metal (BIW, door frames, seat frames): rivet nuts, weld nuts, press-in nuts.
- Suspension joints and safety-critical connections: castle nuts with cotter pins per DIN 935, or ISO 7042 all-metal prevailing torque nuts.
- Engine accessories and high-temperature brackets (above 120°C): all-metal locking nuts; avoid nylon insert types.
- Instrument panels, trim panels, and HVAC ductwork: U nuts with appropriate panel thickness clips.
- Composite or wooden structural components: T nuts with prong anchoring.
Conclusion:
Different types of automotive nuts are used in various vehicle designs and industries. It is difficult to find a nut that will work in every situation. Choosing an automotive nut based solely on its size may lead to a catastrophic joint failure.
Before finalizing your order, make sure that you check compatibility and ensure the thread and strength match your bolt. Evaluate the locking features for joints that face constant vibration. Choose blind or press-in nuts when the panel is not accessible. Lastly, the material and coating must match the environment to prevent corrosion and wear.
CNXD Auto manufactures and supplies a wide range of fasteners, from standard hex to flange nuts to custom designs.
We provide you with a brochure showing the different types of nuts with pictures to help you choose the right ones for your project.
