Locking Nuts

What is locking nuts?

Regular nuts may loosen on their own during use due to vibrations or other factors. To prevent this, self-locking nuts were invented. The primary functions of self-locking nuts are to prevent loosening and resist vibrations, making them suitable for specific applications. Their working principle generally relies on friction to achieve self-locking. Based on their function, self-locking nuts can be classified into types such as those with a nylon insert, those with a crimped neck, and those with a metal anti-loosening mechanism. All of these belong to the category of prevailing torque lock nuts.

How many types of locking nuts?

There are different types of locking nuts, and each works in its own way:

1. Nylon Insert Lock Nuts: These nuts have a nylon collar inserted at the top, which grips the bolt when tightened, creating friction and preventing the nut from loosening.
2. Metal Lock Nuts: These nuts use metal deformation or interference to lock in place. For example, some have a crimped top or distorted threads that create a tight fit.
3. Serrated Lock Nuts: These nuts have serrations on the bearing surface, which dig into the material they are being fastened to, preventing rotation.
4. Castle Nuts (or Slotted Nuts): These are secured with a cotter pin or wire through a slot and hole in the bolt to lock it in place.
5. Prevailing Torque Lock Nuts: These rely on friction in the threads to resist loosening without relying on tension alone.

How to use lock nuts?

To properly use lock nuts, follow these general steps, which may vary depending on the type of lock nut you’re using:

1. Choose the Right Lock Nut

• Select a lock nut appropriate for your application. Some types of lock nuts, like nylon insert lock nuts, are suitable for general use, while others like metal lock nuts or prevailing torque lock nuts are designed for high-vibration environments.

2. Prepare the Bolt or Stud

• Ensure the bolt or stud is clean and free of debris. Threading a lock nut onto dirty or damaged threads can prevent proper locking and may damage the nut or bolt.

3. Align the Lock Nut

• Hand-thread the lock nut onto the bolt, ensuring the nut is aligned properly with the threads. Start by turning the nut by hand to avoid cross-threading.
• For nylon insert lock nuts, the nylon ring should face the bolt or stud end.
• For prevailing torque lock nuts, align the nut’s special thread or deformation to create friction.

4. Tighten the Nut

• Use an appropriate tool such as a wrench or socket to tighten the lock nut. Tighten until snug, and then apply additional torque as needed.
• Do not over-tighten, as this can damage the threads, the nut, or the component. Lock nuts achieve their holding power without needing to be overly tight.

5. Check for Parallel Alignment

• While tightening, ensure that the lock nut and the surface of the part being secured remain parallel to prevent uneven tension or damage to the component.

6. Ensure Proper Locking

• Confirm that the nut does not loosen when subjected to vibration or movement. If you are using a nylon insert lock nut, the nylon ring should grip the bolt threads tightly.
• If you’re using metal locking nuts or prevailing torque nuts, the deformed threads or friction mechanism should resist loosening.

7. Periodically Inspect

• Over time, especially in high-vibration applications, check the lock nut to ensure it remains secure. For reusable types like nylon insert nuts, the nylon may wear out after several uses, so replace them if necessary.

Following these steps will ensure that the lock nut functions as intended, maintaining secure fastening even in environments with vibration or movement.