Last revised: February 10, 2025

Locknuts are a type of prevailing-torque fastener that resists loosening under vibration and torque. They differ from standard nuts because they typically have friction-increasing bearing surfaces (e.g., pitted grooves on flanges) or special internal thread-geometries. In addition to locknut type, these fasteners carry thread specifications and differ in terms of materials of construction, product features, and approvals. Locknuts are available in inch-based and metric designations, and have a numeric (e.g., # 1) or alphanumeric (e.g., M.2) description.

Types 

• Castle nuts are locknuts that have slots or notches that are cut into one end to allow a cotter pin or safety wire to assist in fastening. Castle nuts resemble a chess-playing piece and are also known as castellated or slotted locknuts.
• Distorted-thread locknuts use a deformed section of thread to prevent loosening due to vibration from or rotation of the clamped item. Categories include center-lock, elliptical-offset, top-lock, oval, and non-slotted hex.
• Flex-top locknuts or split-beam locknuts are made from a single piece of material and have a slotted top that expands as the nuts are tightened. This locks them into place and provides vibration resistance.
• Interfering threadnuts or tapered thread nuts are a type of locknut that has an over-sized root diameter to provide permanent or semi-permanent joining.
• Jam nuts are typically half the height of a standard nut. Often, these locknuts are pushed-up or jammed against a standard nut in a fastener assembly to provide an additional securing force.
• Jet nuts or K-nuts are smaller, flanged-type locknuts that are often used in aerospace or automotive racing applications.
• Speed nuts (sheetmetal nuts, tinnerman nuts) can be quickly pushed into place using deformable teeth instead of standard threads.
• Two-piece locknuts are sold as two-component, upper and lower nut assembly pairs.  

Specifications

• Thread direction — Locknuts are available with right-hand (clockwise) or left-hand (counterclockwise) threads.
• Construction material — Some are made of metal materials such as aluminum, brass, bronze, copper, steel, or titanium. They may be anodized, galvanized, nickel-plated, zinc-plated, or treated with other finishes. Non-metallic locknuts made of plastic, rubber, and nylon are also available.
• Non-integral hardware — Locknuts that are sold as an assembly have a non-integral or secondary-material hardware, typically a washer or plastic insert, to improve their mechanical performance. 

Standards                                                                    

DIN 981 — Roller bearings - locknuts

Locknuts FAQs

What are the key specifications and standards engineers should consider when selecting locknuts for a project?

When selecting locknuts for a project, engineers should consider several key specifications and standards to ensure the appropriate choice for their application. Here are some important considerations:

Key Specifications

Material Type: The material of the locknut, such as steel or non-metallic, can affect its performance in different environments.

Thread Type: Ensure compatibility with the mating component, considering thread size and type, such as UNJ threads.

Tensile Strength: Depending on the application, the tensile strength of the locknut is crucial. For example, some standards specify minimum tensile strengths like 1550 MPa or 1210 MPa at ambient temperature.

Locking Mechanism: Different types of locknuts, such as prevailing torque or all-metal, have varying locking mechanisms that can influence their suitability for specific applications.

Relevant Standards

Machine Tool Components: Standards like the one for "C" Type locknuts with socket set screw locking provide guidelines for specific applications.

Prevailing Torque Locknuts: Standards for both inch series and hex locknuts with non-metallic inserts offer specifications for these types of locknuts.

Torque-Type Steel Hexagon Locknuts: This standard provides specifications for steel hexagon locknuts, which are commonly used in various engineering applications.

Rolling Bearings and Locking Devices: Standards related to rolling bearings include specifications for locknuts and locking devices, which are critical in bearing applications.

What are the advantages of using all-metal locknuts over non-metallic ones?

When considering the advantages of using all-metal locknuts over non-metallic ones, several factors come into play. Here are some key advantages:

Advantages of All-Metal Locknuts

Temperature Resistance

All-metal locknuts generally offer superior performance in high-temperature environments compared to non-metallic ones. This is because metal materials can withstand higher temperatures without degrading.

Strength and Durability

All-metal locknuts often have higher tensile strength, making them suitable for applications requiring robust fastening solutions. For instance, they can achieve tensile strengths of 1550 MPa and 1210 MPa, respectively.

Chemical Resistance

Metal locknuts are typically more resistant to various chemicals and solvents, which can be a critical factor in industrial applications where exposure to harsh substances is common.

Reusability

All-metal locknuts can often be reused multiple times without losing their locking capability, unlike some non-metallic locknuts that may degrade or lose effectiveness after repeated use.

Vibration Resistance

The locking mechanisms in all-metal locknuts, such as prevailing torque or other mechanical designs, provide excellent resistance to loosening under vibration, which is essential in dynamic applications.

Considerations

While all-metal locknuts have these advantages, it's important to consider the specific requirements of your application, such as environmental conditions, load requirements, and compatibility with other materials. Non-metallic locknuts might be preferred in applications where weight reduction or electrical insulation is a priority.

What are the different types of locking mechanisms in locknuts?

When discussing the different types of locking mechanisms in locknuts, it's important to understand the various designs and their applications. Here are some common types of locking mechanisms used in locknuts:

Prevailing Torque Locknuts

These locknuts use a design that creates friction between the nut and the bolt threads, maintaining a constant torque that resists loosening. The friction is typically achieved through a deformed section of the nut or an insert, which can be metallic or non-metallic.

All-Metal Locknuts

All-metal locknuts rely on the deformation of the metal itself to create a locking action. This can include designs like distorted thread locknuts, where the threads are intentionally deformed to increase friction. These are known for their high temperature and chemical resistance.

Non-Metallic Insert Locknuts

These locknuts use a non-metallic insert, such as nylon, to create friction against the bolt threads. The insert deforms slightly as the nut is tightened, providing a locking action.

Torque-Type Locknuts

Torque-type locknuts are designed to provide a specific torque resistance. They often feature a prevailing torque mechanism and are commonly used in applications where precise torque control is necessary.

Locknuts with Set Screw Locking

These locknuts use a set screw to lock the nut in place. The set screw is tightened against the bolt or shaft, providing additional security against loosening.

Each type of locking mechanism has its own advantages and is suited to different applications depending on factors like temperature, chemical exposure, and vibration. For specific applications, engineers should refer to the relevant standards to ensure the locknut meets the necessary requirements.

What are the differences between prevailing torque and all-metal locknuts?

When comparing prevailing torque locknuts and all-metal locknuts, there are several key differences to consider, particularly in terms of their design and applications:

Prevailing Torque Locknuts

Design and Mechanism

Prevailing torque locknuts create friction between the nut and the bolt threads to maintain a constant torque that resists loosening. This is typically achieved through a deformed section of the nut or an insert, which can be metallic or non-metallic.

Applications

These locknuts are suitable for applications where maintaining a consistent torque is crucial, and they are commonly used in dynamic environments where vibration is a concern.

Materials

Prevailing torque locknuts can include non-metallic inserts, such as nylon, which provide additional friction.

All-Metal Locknuts

Design and Mechanism

All-metal locknuts rely on the deformation of the metal itself to create a locking action. This can include designs like distorted thread locknuts, where the threads are intentionally deformed to increase friction.

They are known for their high temperature and chemical resistance.

Applications

These locknuts are ideal for high-temperature environments and applications where chemical resistance is necessary. They are also suitable for situations where reusability is important, as they can often be reused without losing their locking capability.

Materials

All-metal locknuts are made entirely of metal, which provides superior strength and durability compared to non-metallic options.

What are the advantages of using torque-type locknuts in high-vibration environments?

Torque-type locknuts offer several advantages in high-vibration environments due to their specific design and mechanism. Here are some key benefits:

Advantages of Torque-Type Locknuts in High-Vibration Environments

Consistent Torque Control

Torque-type locknuts are designed to maintain a specific resistance to turning, known as prevailing torque. This ensures that the nut remains securely fastened even under dynamic conditions, which is crucial in high-vibration environments.

Controlled Friction

The design of these locknuts includes features that control the amount of friction applied during installation. This controlled friction helps maintain the desired torque level, preventing the nut from loosening due to vibrations.

Durability and Material Strength

Typically made from robust materials, torque-type locknuts can withstand the stresses of repeated torque applications. This durability ensures that the locking mechanism remains effective over time, even in challenging conditions.

Resistance to Loosening

The prevailing torque mechanism provides excellent resistance to loosening, which is essential in environments where vibration is a significant concern. This makes them suitable for applications in machinery and automotive industries where high vibration is common.

How does the prevailing torque mechanism work?

Detailed Explanation of the Prevailing Torque Mechanism

The prevailing torque mechanism in locknuts is designed to resist loosening under dynamic conditions, such as vibration or thermal cycling. Here's how it works in detail:

Friction-Based Locking

Prevailing torque locknuts create friction between the nut and the bolt threads. This friction is achieved through a specific design that maintains a constant torque, preventing the nut from loosening.

Deformed Section or Insert

The friction is typically generated by a deformed section of the nut or an insert. This can be a metallic or non-metallic component that interacts with the bolt threads to increase resistance to turning.

For example, non-metallic inserts, such as nylon, are used in some designs to provide additional friction.

Material and Design Considerations

The materials used in prevailing torque locknuts are chosen for their ability to withstand the stresses of repeated torque applications. This ensures that the locking mechanism remains effective over time.

The design may include features such as distorted threads or specific geometries that enhance the locking action.

Applications

These locknuts are particularly useful in applications where maintaining a consistent torque is crucial, such as in machinery and automotive industries. They are effective in environments where vibration is a concern, as they provide excellent resistance to loosening.

Locknuts Media Gallery

References

Electronics360—Heilind Electronics supplies Alpha Wire’s cable glands

Image credits:

Altech Corp. | MISUMI USA | Fastener SuperStore, Inc.