How To Remove Stubborn Locking Nuts

Locking nuts are designed to resist loosening under torque or vibration forces. They are manufactured and machined in a way that prevents them from easily backing off once screwed on. This is achieved through increased friction, often via threading designs, or through a locking device or mechanism. However, locking nuts can sometimes be challenging to remove, and special tools or techniques may be required. In some cases, the locking nut may still be in place even after the screw has been removed, requiring additional steps to fully detach it.

The locking nut is stuck due to thread galling

Thread galling is a common issue with locknuts and other threaded fasteners. It occurs when friction and adhesion between the male and female threads break down the coating, leading to increased friction and, in some cases, fusion. This phenomenon is sometimes referred to as "cold welding". While the exact cause of galling remains a mystery, certain factors can contribute to its occurrence.

Galling typically happens during the tightening of stainless steel locknuts, but it can also occur in aluminium or titanium assemblies. These materials have high friction coefficients, making them more susceptible to galling. Stainless steel screws, in particular, have a higher coefficient of friction, lower rate of thermal conductivity, and larger expansion coefficients, making it easier for the male and female threads to adhere to each other.

To prevent thread galling, there are several measures that can be taken:

• Slow down the installation speed: Reducing the speed will lower the friction and heat generated, making it less likely for the nut and bolt to seize.
• Lubricate the threads: Using a suitable lubricant can reduce the chances of galling. However, it is important to consider the end use of the assembly and choose a lubricant that is compatible.
• Avoid using different alloys: Consult with a representative to find metals that work well together and have a lower chance of galling.
• Stop if the assembly begins to seize: If galling occurs, stop tightening and allow the assembly to cool down. Then, carefully remove the nut and check for damage.
• Use clean parts: Ensure that there is no debris or dirt inside the threading, as this can increase friction during installation. Compressed air can be used to ensure a clean surface.
• Inspect for foreign matter: Foreign matter, such as burrs, can cause galling. A burr is a raised edge or small piece of material stuck on the thread, usually resulting from the thread-rolling process.
• Check for damaged threading: Any damage to the threading will increase friction during installation, making galling more likely.

By following these preventative measures, you can reduce the chances of thread galling and keep your locknuts and fasteners in good working condition.

The locking nut is a self-locking nut

A lock nut, also known as a locking nut or self-locking nut, is a type of fastener that is designed to achieve a secure fixing. They are screwed onto a bolt or threaded rod like a standard nut, but they resist loosening under torque or vibration. This makes them especially useful in applications where the bolt or nut assembly will be subject to vibrating or torque forces while installed, such as engines and automotive parts.

Lock nuts were invented in the 1930s to reduce the cost of nut and washer use in machine assemblies. Before this, the best way to prevent nuts from loosening due to vibration was to use two standard nuts on a single bolt. However, this doubled the cost of nuts and washers for each bolt. While individual lock nuts are more expensive than non-locking versions, they are still a more cost-effective solution than using two standard nuts.

There are two main types of locking nuts: those that use friction and those that use a positive locking device. Friction-based locking nuts are designed with pitted or flanged grooves and require more torque to tighten and loosen. They don't spin freely along the fastener's shaft, as they begin to clamp down as they are rotated. This makes the assembly process longer but they are less expensive.

Positive locking nuts, on the other hand, rotate easily during tightening and loosening for faster assembly. They are locked into position by a positive action, such as inserting a pin or crimping a small lip or crown inward when installed to grip the shaft. While assembly is faster and more secure, this type of lock nut is more costly.

Nylon insert lock nuts, also known as Nyloc nuts, are a popular and widely used type of locking nut. They feature an inner sleeve made of nylon plastic that deforms around the bolt threads, creating binding friction. As the sleeve deforms, they become less reusable. They are commonly used in applications such as domestic appliances and automotive repair.

Another type of lock nut is the jam nut, which is thinner and designed to be tightened or "jammed" against another nut. Jam nuts are not considered best practice in industrial applications as predicting loads under stress is difficult. However, they can be useful in areas with restricted space where a full-sized nut cannot be used.

The locking nut is a nylon insert lock nut

Nyloc nuts are commonly used in applications such as elevators, streetlights, furniture, lifting equipment, and pipelines. They are also suitable for use with metal screws, as in the case of the nylon hex lock nut, which includes a flange that acts as a built-in washer. This helps to spread the forces under the nut head over a larger area, reducing the chance of damage to the surface while securing it in place.

Nyloc nuts are available in different materials, such as zinc-plated steel and stainless steel, and can be purchased from hardware stores or online retailers. They are a popular choice due to their effectiveness in preventing loosening and their economic price point.

When working with nyloc nuts, it is important to note that they may require more force or torque to tighten and loosen compared to other types of nuts. Additionally, there is some debate on whether nyloc nuts should be reused, as they may weaken with each use. In applications where safety is critical, it is recommended to use new nyloc nuts.

The locking nut is a surface bearing lock nut

Locking nuts are used to achieve a secure fixing and are designed to resist loosening under torque or vibration forces. They are commonly used in engines and other automotive parts.

There are two main categories of lock nuts: prevailing torque nuts and surface bearing lock nuts. This answer will focus on the latter.

Surface bearing lock nuts spin freely under normal circumstances but can be tightened against a bearing surface to activate a locking mechanism that holds them firmly in place. An example of this type of lock nut is the nylon insert lock nut, which features an inner sleeve that moulds to the threading pattern. As the sleeve of a nylon insert lock nut deforms on attachment, they are less reusable than some other types. They are, however, useful for securely joining softer materials like wood and plastic without the risk of over-tightening and damaging the surface of the material. They are also good at resisting vibration loosening and are often used in applications like domestic appliances and automotive repair.

Another example of a surface bearing lock nut is the hex jam nut, which is effectively a double-nut system where two pieces are tightened against one another.

The locking nut is a prevailing torque nut

A locknut, also known as a locking nut, is a nut that resists loosening under vibrations and torque. The locking nut is a prevailing torque nut, which means it relies on the principle of prevailing torque to resist vibration loosening. Prevailing torque is the amount of force required to run the nut down the threaded shaft of a bolt or screwed rod, ensuring the nut grips tightly and does not back off easily.

Prevailing torque nuts have a portion of the nut that deforms elastically to provide a locking action. They are designed to create prevailing torque through various mechanisms. For example, conical flange lock nuts are designed to create prevailing torque through their shape, while other lock nuts, such as Stover lock nuts, have a crimpable section that is designed to be crimped around a bolt shaft to create enough prevailing torque to hold the lock nut in place.

Specific examples of prevailing torque lock nuts include conical lock nuts, tri-lock nuts, top lock, Stover lock nut, and Griptite nuts. Most are all-metal lock nuts, and many have some sort of lip or crown that is designed to be crimped around a bolt shaft after installation.

When it comes to installation, some lock nuts need to be wrenched in a specific direction, while others may require a lock nut washer alongside the nut itself to achieve the full lock.

Frequently asked questions