Nuts can be used as a fastener in many situations, but in some contexts, you need to think about what is actually keeping the nut in place. For basic nuts, the only thing keeping the nut there is a small amount of friction, a slight stretching of the bolt, and a bit of compression. If that nut is subjected to vibration or other forces, it’s eventually going to loosen. Sometimes you need something to keep that nut in place, and that’s where lock nuts come in.

What is a lock nut?

Lock nuts are used in situations where vibration or rotation would cause a normal nut to loosen. They may be used on machines (think washing machines, power tools) or vehicles (think bikes, cars, aeroplanes), and they create additional friction to stop the nut from loosening by a range of different methods. Lock nuts are also known as locknuts, prevailing torque nuts, stiff nuts, or elastic stop nuts.

Lock nut types

There are a few different lock nut types available depending on your needs and specific use. Here are five common types.

Jam nut

A jam nut is used next to a standard nut, ‘jamming’ it so that it is locked in place. A jam nut stops a nut from loosening because it is screwed against the other nut, preventing it from moving. A half nut, also known as thin nut, is a type of jam nut that is half the thickness.

Jam nuts have a couple of applications. One application is when a nut needs to be secured, but can’t be clamped against another object. Jam nuts can also be used to rotate threaded rod. As threaded rod doesn’t have a bolt head, a pair of jam nuts tightened against each other create a point where a wrench can be used.

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Split beam nut

A split beam nut is a lock nut which has slots cut into the top, enabling portions of the nut to be bent inwards. The inward bend means extra friction is created as the nut is screwed on and the sections are pushed back.

One of the benefits of split beam nuts is that high strength grades can continue to function at high temperatures. Nylon-insert or Nyloc nuts, on the other hand, only retain their locking ability up to 121 °C. Aerotight is one of the most common and popular brands of split beam nuts.

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Nyloc nut

A Nyloc nut is a locking nut that has a nylon insert at the end which is slightly smaller than the diameter of the screw. The nylon insert deforms over the thread of the screw, creating friction which locks the nut in place. The side of the nut without the nylon ring is threaded onto the bolt first.

There is some disagreement over whether Nyloc nuts can be reused. The nylon ring returns to its original shape after being unscrewed, but for some critical aviation applications reuse is not permitted. Nyloc is the brand name of the most popular nylon locknut.

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Serrated flange nut

A serrated flange nut is a locking nut with a wide flange at one end which functions as an integrated washer. The serrations are angled in such a way that they prevent the nut from loosening.

The serrated flange means that these nuts must not be used with a washer. The serrations scratch the surface they are screwed against, so it may not be appropriate for applications where the surface must remain unblemished.

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Philidas nut

A Philidas nut is a type of lock nut which displaces or ‘axially de-pitches’ the thread in the last one or two turns. This increases the friction between the thread and the nut. Although similar in appearance to split beam nuts, Philidas nuts use a fundamentally different method of locking. Because Philidas nuts displace the thread, they can be classed as a type of distorted thread locknut.

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Alternatives to lock nuts

There are a few alternatives to lock nuts which use different methods of locking and may, therefore, be categorised differently. These include castellated nuts (also known as castle nuts), thread-locking fluid, oval-shaped nuts, and safety wire.

Buy lock nuts online

Shop4Fasteners stock an extensive range of nuts and fasteners. Check out our full range of nuts. Can’t find what you’re looking for? Please get in touch and we’ll do our best to supply it to you.