Nuts Designed to Resist Loosening Under Vibration & Toque
Lock Nuts, also known under many other names such as locknuts, locking nuts, self-locking nuts, prevailing torque nuts, stiff nut, elastic stop nut, are special kinds of nuts that resist loosening. Specifically, loosening from vibration and torque.
When working with fasteners, the last thing anyone wants is for the assembly to become undone over time. This is especially true in applications where a person's well-being could be at risk. So lock nuts exist to help prevent potential disasters from occurring for applications frequently subject to vibrations and torquing from outside sources.
There are a variety of lock nuts available. Each uses a different locking method to prevent loosening.
Locking Nuts for use with a Cotter Pin or Safety Wire
Castle nuts are used in conjunction with a cotter pin to prevent loosening. This nut has slots (notches) cut into one end. The name comes from the nut's resemblance to the parapets of a castle. The bolt or axle has one or two holes drilled through its threaded end. If the castle nut's slot isn't aligned with the bolt or axle's hole, the nut is rotated to the nearest slot. The nut is then secured with a cotter pin or safety wire. Castellated nuts are used in low-torque applications, such as holding a wheel bearing in place.
Castle nuts are available in 18-8 Stainless Steel and Brass.
Keps K Lock Nuts
Hex Nuts with an Attached Free-Spinning Washer
Keps knut lock nuts are nuts with an attached, free-spinning washer. It is used to make the assembly more convenient. K locknuts feature a conical external tooth washer attached to the bottom of the nut.
Keps K lock nuts are available in 18-8 Stainless Steel and Zinc Plated Steel.
Non-Serrated Hex Flange Cone Locking Nuts
Hex Nuts with an Integral Washer & Rounded Locking Top
Hex flange cone locking nuts are like stover nuts but feature a built-in, non-spinning, non-serrated flange designed to act similarly to a washer during installations. This flange spreads the load placed on the nut over a wider surface area to prevent damaging the installation material. They also save time during installations by eliminating the need to install a separate washer entirely. The conical top features imperfect threading to resist shock and vibration from loosening the nut.
Non-serrated hex flange cone locking nuts are available in Plain Steel.
Nylon Insert Lock Nuts
Lock Nuts with a Nylon Insert Stopper
A nylon insert lock nut is a hex-shaped, internally threaded nut with a nylon insert. The nylon material prevents loosening from vibration and cross threads to stop the nut from backing off the fastener. The insert deforms elastically over the threads of the screw, but threads are not cut into the nylon. The nylon insert locks the nut in two ways. First, it forces the bottom face of the screw threads against the nut threads' top face, increasing the friction between them. Second, the nylon applies a compressive force against the screw itself.
Nylon lock nuts also come in a waxed variety. A standard nylon lock nut generates more heat when being installed. The waxed version helps to prevent galling when installing the nuts.
Nylon insert lock nuts are available in 18-8 Stainless Steel, 316 Stainless Steel, Zinc Plated Steel, Brass, Aluminum, Chrome Plated Steel, and Black Chrome Plated Steel.
Slotted Hex Nuts
Hex Nuts Designed for Use with Cotter Pins
Slotted Hex Nuts are nuts with slots protruding from the top, like castle nuts. To use a slotted nut, a hole is drilled through the threaded portion of a bolt or stud. A cotter pin is then placed through the slots and hole and deformed so it cannot easily be removed. This creates a locking effect that prevents the nut from spinning free of the bolt or stud.
Slotted nuts are generally preferred because they have a lower profile than a castle nut of the same size.
Slotted nuts are available in Plain Steel.
Prevailing Torque Lock Nuts
Prevailing torque lock nuts (commonly known as stover lock nuts) have a rounded top and a flat bottom. The threads near the top are intentionally imperfect to add shock and vibration resistance. Stover nuts are wax treated to prevent galling from occurring during the installation.
Stover nuts are available in Zinc Plated Steel.
Two Way Reversible Lock Nuts
Hex Centerlock All Metal Lock Nuts
Two-way reversible lock nuts (also known as Centerlock Nuts) get their name because of their functionality and ability to be used either top-up or top-down. Two Way Lock Nuts feature indentations on the nut's outside flats, distorting the internal threads to increase resistance on the mating part. This creates a locking mechanism in the center of the nut.
Having the locking portion within the hex nut offers several benefits, including versatility in application, application speed (which helps on assembly lines), and application environment versatility. All metal lock nuts can be used in high heat or highly corrosive applications where a nylon insert would not be suitable. Bolts or screws used with two way reversible lock nuts can also be shorter than the nut because the locking occurs in the center. For this reason, the end of the bolt or screw does not have to extend beyond the end of the nut.
Two-way reversible lock nuts are available in 18-8 Stainless Steel, 316 Stainless Steel, and Zinc Plated Steel.
What are locking nuts for?
Lock nuts are an easy to use, cost-effective solution to protecting against vibration-related loosening. They're used to protect applications from loosening over time.
How do you use lock nuts?
Most lock nuts are used the same way traditional nuts are; by simply fastening them to the opposite side of a bolt. The locking action activates after the nut is fastened down. The exception to this is castellated nuts and slotted nuts, which needs a hole drilled into the bolt and a cotter pin to finish installation.
Can lock nuts be removed?
They're not designed to be removed easily. If they were, they wouldn't be very good lock nuts! That said, it is possible to remove locknuts. It may require some patience and, in some cases, power tools to remove them. The exact method will vary based on application and lock nut.
Do you need a lock washer with a lock nut?
No, you don't need a locking washer to use a locking nut or vice versa. Most applications will call for using one or the other, not both. That's not to say you can't use both a lock nut and lock washer as part of the same assembly. It's just not common to do so; one will suffice for most jobs.
Which way do lock nuts go?
Lock nuts should sit flush with the material surface. Nylon insert nuts, castle nuts, slotted nuts, and stover nuts should have their various locking protrusions facing away from the installation material. Keps K-lock nuts will have the washer facing towards the installation material.
Can you reuse self locking nuts?
Yes and no. Self-locking nuts and most lock nuts, in general, can be reused. However, repeated use will wear down the nut's locking ability, making it less effective on subsequent installation. It's generally better to use new lock nuts instead of reusing old ones.