What Is Locknut?- Definition, Types & How it works

What is Locknut?

Locknuts are internally threaded fastener that possesses locking capabilities either by themselves or in concert with another component. By design, lock nuts are engineered to resist loosening when subjected to vibration or torque.

A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut, stiff nut, or elastic stop nut, is a nut that resists loosening under vibrations and torque.

Elastic stop nuts and prevailing torque nuts are of the particular type where some portion of the nut deforms elastically to provide a locking action. The first type used fiber instead of nylon and was invented in 1931.

Locknuts, jam nuts, lock washers, and thread-locking fluid are ways to prevent vibration from loosening a bolted joint.

Lock Nuts with Nylon Inserts

Locknuts with nylon inserts (self‑locking nut, locking nut) are a prevailing torque, locking nut that resists loosening caused by vibration and normal use. Unlike free spinning nuts, lock nuts make use of a deforming elastic or metal material to stay in position against torque and shock.

Locknuts with nylon inserts are a popular solution for many applications, however, they are limited to applications exposed to temperatures under 250°.

How Do Lock Nuts with Nylon Inserts Work?

Hex lock nuts use a nylon insert at the top of the nut creating tension between the nut and the threads of the mating component. As the nut is threaded onto a shaft or rod, it will spin freely until the threads from the host part engage the nylon insert.

The threads of the mating shaft will displace the nylon and create resistance. This resistance prevents unintentional moving of the lock nut. The nylon in traditional hex lock nuts can wear and become less effective after repeated removal and installation. For optimum holding power, replace the nut if it needs to be removed during the disassembly of a component.

Types of Lock nut

There are various kinds of specialized lock nuts, including

  1. Jam nut
  2. Castellated nut or Castle nut
  3. Sawn nut
  4. Penn, ring, or grooved nut
  5. Locking with pin
  6. Locking with plate
  7. Spring lock washer

1. Jam Nut

A jam nut is a low-profile nut that is usually half the size of a standard nut. It is commonly used as a type of lock nut where it is “jammed” up against a standard nut to secure the two in place. It is also used in situations where a standard nut would not fit.

The term “jam nut” can also refer to any nut that is used in the same function (even a standard nut that is used for jamming purposes). Jam nuts, other types of lock nuts, lock washers, and thread-locking fluid prevent vibrations from loosening a bolted joint.

A jam nut is often used when a nut needs to be locked into place without clamping against another object. The jam nut essentially acts as “another object” as the two nuts are tightened against each other. They can also be used to attach an object to a fastener without applying force to that object.

This is accomplished by first tightening one of the nuts on the item. Then the other nut is screwed on top of the first nut. The inner nut is then loosened and tightened against the outer nut.

Jam nuts can also be used in situations where a threaded rod needs to be turned. Since threaded rods do not have screw heads, it is difficult or impossible to apply torque to a threaded rod. A pair of jam nuts are used to create a point where a wrench can be used.

Jam nuts can be unreliable under significant loads. When the inner nut is tightened more than the outer nut, the outer nut can give way. When the outer nut is tightened more than the inner nut, the inner nut can loosen.

Locknut

2. Castellated nut or Castle Nut

A castellated nut, sometimes called a castle nut, is a nut with slots (notches) cut into one end. The name comes from the similarity of the nut the crenellated parapet of a medieval castle. Castellated nuts are sometimes mistakenly called castigated nuts.

While castellated nuts are often referred to as slotted nuts, slotted nuts differ slightly from castellated nuts from a technical point of view. Castellated nuts are formed with a round section at the top where the slots are located. Slotted nuts do not have this rounded modification. The flat sides of the slotted nuts extend completely from the top to the bottom of the nut.

Both castellated and slotted nuts are designed using a pin (usually a cotter pin) that fits through the slots and through a hole in the screw that the nut attaches to. This pin prevents the nut from turning and loosening. Compared to slotted nuts, castellated nuts allow the cotter pin to be attached closer to the edges of the nut itself, which provides additional security.

The bolt has one or two holes drilled through its threaded end. The mother is properly dressed. If the slot is not aligned with the hole in the fastener, the nut is rotated forward to the next slot. The nut is then secured with a cotter pin, an R-clip, or a safety wire. It’s a positive lock.

Castellated nuts are used in low-torque applications, such as holding a wheel bearing in place.

3. Sawn locknut

The sawn nut has a slot sawn halfway through. After the nut is screwed down, the small screw is tightened which produces more friction between the nut and the bolt. This prevents the loosening of the nut.

4. Ring Nut, Penn nut, or Grooved Nut

It has an upper portion hexagonal and a lower part cylindrical. It is largely used where bolts pass through connected pieces reasonably near their edges such as in marine-type connecting rod ends.

The bottom portion is cylindrical and is recessed to receive the tip of the locking set screw. The bolt hole requires counter-boring to receive the cylindrical portion of the nut. In order to prevent bruising of the latter by the case-hardened tip of the set screw, it is recessed.

5. Locking with Pin

The nuts may be locked by means of a taper pin or cotter pin passing through the middle of the nut. But a split pin is often driven through the bolt above the nut.

6. Locking with plate

These come in the form of thin metal plates. With the help of a set-screw, its rotation is retained round a nut after the nut has been tightened. The plate consists of a hole which may be usually a twelve-sided one for enabling easy adjustments.

The set screw used for securing the locking plate is kept intact with a spring washer. Double-sided locking plates are also available and are used for locking two nuts simultaneously.

7. Spring Locknut Washer

As the nut tightens the washer against the piece below, one edge of the washer is caused to dig itself into that piece, thus increasing the resistance so that the nut will not loosen so easily. There are many kinds of spring lock washers manufactured, some of which are fairly effective.

A regular nut may also be locknut by applying a thread locker or by drilling and pinning.

FAQs.

What is Locknut?

A locknut, also known as a lock nut, locking nut, self-locking nut, prevailing torque nut, stiff nut, or elastic stop nut, is a nut that resists loosening under vibrations and torque.

What are the Types of Locknuts?

There are various kinds of specialized lock nuts, including:

  1. Jam nut
  2. Castellated nut or Castle nut
  3. Sawn nut
  4. Penn, ring, or grooved nut
  5. Locking with pin
  6. Locking with plate
  7. Spring lock washer

What are locking Devices?

Locking devices are a device that is used in conjunction with fasteners to positively lock the fastener. This means that the fastening element cannot loosen due to vibrations. The security of an entire system often depends on locking devices.

What is Jam Nut?

A jam nut is a low-profile type of nut, typically half as tall as a standard nut. It is commonly used as a type of locknut, where it is “jammed” up against a standard nut to lock the two in place. It is also used in situations where a standard nut would not fit.

What is Castellated nut?

A castellated nut sometimes referred to as a castle nut, is a nut with slots (notches) cut into one end. The name comes from the nut’s resemblance to the crenelated parapet of a medieval castle.

What does a lock nut do?

Locknuts are internally threaded fastener that possesses locking capabilities either by themselves or in concert with another component. By design, lock nuts are engineered to resist loosening when subjected to vibration or torque.

What is the difference between a lock nut and a regular nut?

Traditional nuts simply consist of a basic threaded hole, so constant exposure to vibrations can knock them loose from the bolt-on which they are placed. Locknuts protect against loosening, however, by featuring a design that increases the nut’s resistance to vibrations.

What is the difference between a hex nut and a lock nut?

A hexagon nut is a standard fastener and one of the most basic fastening solutions. It’s not technically a locking nut, but by using two nuts together (typically one standard hexagon nut and a thin hexagon nut) they act as a type of locknut but have limited resistance to loosening under vibration.

How do you loosen a plastic wing nut?

Use Heat or Calcium Dissolver. Whether you use a basin wrench or a hammer and screwdriver, the nut is easier to loosen if you heat it with a hairdryer. The heat should soften the plastic and make the nut pliable enough to break free.

Why use a washer with a screw?

The primary purpose of most washers is to evenly distribute the load of the threaded fastener with which they are used. Threaded fasteners stress the material in which they are driven. Driving a screw into wood, for example, may cause the wood to crack around the surface.

Do you have to use a flat washer with a lock washer?

It’s useless if you do. A lock washer is designed to press into the surface of the nut and whatever is being fastened. Flat washers spread out the load of the tension to prevent pull-through or bending what’s being fastened but make lock washers useless.

How do Flexloc nuts work?

Flexloc nuts spin freely until the mating threads enter the top locking area. As the nut is wrenched into position, the slotted section expands and locks the nut. Full thread engagement occurs when 1 1/2 threads of a standard bolt extend beyond the top of the nut.

Should you use a lock washer with a lock nut?

Place the lock washer between the nut and the work surface if using a nut-and-bolt configuration, or between the fastener head and the work surface if using a tapped hole configuration. In other words, the bolt goes straight into the hole and doesn’t poke out the other end, so no nut is used.

How does a Floyd Rose nut work?

A Floyd Rose lets you lock the strings in place at two points on your guitar – at the bridge itself, and at the nut. The bridge features locking saddles, which the strings are inserted into. These are then fixed into place via tightening bolts on the back of the bridge, which are adjustable with an Allen key.

What is the difference between a castle nut and a slotted nut?

The difference between a slotted nut and a castle nut is the latter has turret geometry on the top of the nut. The nut thicknesses are the same as a slotted nut. Like slotted nuts, castle nut applications are similar using steel pins and taper or split pins, to lock the nut into position after tightening.

What is a half lock nut?

Also known as a half nut, thin nut, or jam/lock nut. Typically fitted with a spanner or ratchet with socket, often used in pairs or in conjunction with a hexagon full nut in a locking arrangement. A popular nut type, and used for decades on all types of assembly throughout the world.

Is there a tool for tightening wing nuts?

Steel wing nut driver is a tool that works with any power drill. It is designed to fit over wing nut wings to enable you to tighten or loosen wing nuts quickly when installing hurricane panels.

How do you unscrew a rusted wing nut?

Place the tip of a flat-head screwdriver against the right side of one wing. Tap the end of the screwdriver to get the wing nut to start rotating counterclockwise. Once the wing nut begins to turn, twist it counterclockwise by hand until it is off the threaded shaft.