Locknut: Definition, Types and How does it work?

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 will resist 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.

A lock nut is a nut that will resist loosening under vibration and torque. There are many types of lock nut but they can be broadly divided into those which use friction to prevent loosening and those that have some form of positive locking device. 

Locknuts that use friction to resist loosening usually require a greater torque to both tighten and loosen, especially during the initial free rotation before they start to clamp down on the part. This means that they cannot be spun rapidly along a long length of thread, greatly increasing manual assembly time.

Positive Locking Nuts

Locknuts that use a positive locking device can be freely rotated to both tighten and loosen, they only lock when positive action is performed to lock them in their current position, such as inserting a pin. This can enable both more rapid assembly and more secure fastening.

The following is a list of positive locking nuts

  1. Jam nut or lock nut
  2. 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 purpose). 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 thread locker or by drilling and pinning.

FAQs.

What is Locknut?

A lock nut is a nut that will resist loosening under vibration and torque. There are many types of lock nut but they can be broadly divided into those which use friction to prevent loosening and those that have some form of positive locking device. 

What is 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 crenellated parapet of a medieval castle.