A Complete Guide to Locking Nuts

There are numerous different lock nut types widely sold online in the UK. They broadly fall into two main categories, known as prevailing torque nuts and surface bearing lock nuts.

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Prevailing Torque Nuts

A prevailing torque lock nut relies on the principle of prevailing torque to resist vibration loosening. In this context, prevailing torque is the amount of force required to run the nut down the threaded shaft of a bolt or screwed rod, such that the nut grips tightly and does not back off easily.

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. This crimping process is what creates enough prevailing torque to hold the lock nut in place, even during heavy vibration.

However, not all prevailing torque or all-metal nuts will have a crimpable section. Some are designed to create prevailing torque through different mechanisms, such as conical flange lock nuts. Many of these types of nuts will need to be wrenched in either direction, whether installing or removing them.

Surface Bearing Lock Nuts

A surface bearing locking nut spins freely under normal circumstances, but that can be tightened against a bearing surface to activate a locking mechanism that holds it firmly in place.

Frequently bought examples of lock nut types in widespread use include:

• Nylon insert lock nuts - featuring an inner sleeve that moulds to the threading pattern
• Hex jam nuts - effectively a double-nut system, in which two pieces are tightened against one another
• Prevailing torque or Stover locking nuts
• Centre locknuts (also known as two-way locking nuts) - a common subtype of distorted thread nuts, where the nut threading is deliberately designed to interfere with and ultimately bind against the bolt threading
• Serrated flange lock nuts - another subtype of distorted thread locking nuts
• Top lock nuts
• Jet nuts or K-lock nuts
• Castellated or castle-lock nuts

The best locking nuts for your needs will depend on the various specifics of the task at hand. Important things to consider include:

• Thread direction - lock nuts can be bought with clockwise (right-hand) or anticlockwise (left-hand) threading
• The size of stiffnuts you require, in metric or imperial standards
• The type of assembly they are being used with and the environment that a locking nut will be exposed to during its working life
• Whether or not the nut you choose requires any secondary components, such as a specific washer, to lock properly
• The material your locking nut is made from

There are several subsets of the main types available, as well as a few more specialised models for highly specific applications. Some of the more popular variants are defined below.

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