Locking nuts, or self-locking nuts, are used with threaded fasteners and designed to resist loosening over time.
Vibrations, thermal variations and changes in load can cause bolts to come loose over time, but the clamp force can be maintained by using a range of lock nut types.
Widely used across engineering and manufacturing, including across the rail and automotive sectors, locking nuts help to ensure bolted joints remain strong and durable when under continued stress.
Using the right type of locking nut for the right purpose is crucial, and in this blog we will talk you through the different options.
What is a lock nut
A locking or self-locking nut is designed to resist rotation through a variety of mechanisms. The anti-rotation mechanism is built into the nut to increase friction and prevent loosening over time.
Standard nuts without such features are susceptible to movement over time, especially in environments subject to vibration and movement. Common applications include:
- Automotive assemblies
- Railways
- Industrial machinery
- HVAC systems
- Agricultural equipment
- Electrical enclosures
The main benefit of locking nuts therefore is that they continue to hold the bolt in place reliably, even in extreme conditions, making them suitable for a wide range of heavy mechanical applications. With improved safety, reduced maintenance and greater reliability, they are a mainstay in construction, manufacturing and engineering.
At this point, it is important to make a clear distinction between a locking / self-locking nut and a lock nut. Lock nuts, often referred to as hexagon half-nuts, are used in pairs to perform a similar locking feature.
How do lock nuts work
Below is an overview of the main locking mechanisms:
- Nylon insert locking – a nylon ring insert grips the bolt thread, creating friction and resisting loosening (e.g. Nyloc nuts).
- Prevailing torque locking – the nut maintains resistance while being threaded onto the bolt, creating continuous locking force (e.g. Philidas and Aerotight nuts).
- Metal deformation locking – portions of the nut are intentionally deformed to grip the corresponding thread
- Friction-based locking – additional friction is created between the nut and mating surface (e.g. serrated flange nuts).
These mechanisms improve resistance to vibration, help prevent loosening and increase overall assembly reliability.
Common lock nut types
Common locking nuts and fastening nuts with locking or retention features include:
| Locking Nut Type | Locking Method | Advantages | Typical Applications |
| Nyloc Nuts | Nylon insert | Cost-effective, easy to install | Automotive, machinery, general engineering |
| Philidas Nuts | Prevailing torque | Reusable, vibration resistant | Rail, defence, heavy engineering |
| Aerotight Nuts | Metal deformation | High temperature performance | Aerospace, industrial equipment |
| Prevailing Torque Nuts | Mechanical friction | Reliable locking performance | Manufacturing and industrial assemblies |
| Serrated Flange Nuts | Serration grips bolt surface | No washer required | Automotive and equipment manufacture |
| Cage Nuts | Captive nut in spring steel cage | Easy panel installation | Server racks, enclosures, cabinets |
| Knurled Nuts | Hand-tightened grip surface | Quick installation and adjustment | Electronics and light-duty assemblies |
See our whole range of locking nuts.
Lock Nut Materials and Finishes
Locking nuts come in a variety of materials and finishes to suit a range of applications, including:
- Stainless steel – Offers excellent corrosion resistance and durability, making it ideal for outdoor, marine and hygienic environments where long-term performance is required.
- Carbon steel – Provides high strength and load-bearing capability at a cost-effective price point, making it a popular choice for general engineering and industrial applications.
- Brass – Combines good corrosion resistance with non-magnetic properties, making it well suited to electrical, plumbing and decorative applications.
- Zinc-plated finishes – A protective zinc coating improves corrosion resistance and extends lifespan.
How to Choose the Right Lock Nut
Choosing the right self-locking nut depends on the specific application. Consideration must be applied to the load, the level of vibration, operating temperature and environmental conditions. Material compatibility is also important to prevent corrosion and ensure reliable performance.
For safety-critical applications, additional security requirements may influence the choice of locking mechanism. It’s also worth considering future maintenance, as some locking nuts are better suited to repeated removal and reinstallation than others. Selecting the right nut helps improve reliability, safety and lifespan.
How to Install Lock Nuts Correctly
The correct nut and bolt combination is crucial to the performance of the locking nut, which needs to be tightened to the recommended torque. Avoid over-tightening, as this can damage threads or reduce the effectiveness of the locking feature.
Some self-locking nuts, particularly nylon insert types, may lose performance after repeated use, so replacement should be considered during maintenance. Regular inspections can also help identify wear, corrosion or damage before it affects assembly reliability.
Choosing the right lock nut types for your project is a crucial step. If you need a reliable and durable bolted joint, locking and self-locking nuts come in a variety of styles and materials depending on the application and conditions.
The friendly team at Fastenright can advise you on selecting the locking nuts for your needs. Contact us to discuss your project today.
