What are Cotter Pins? Definition, Working, Types, Installation & How to Use?


Split pins, also known as cotter pins, are metal fasteners with two tines that bend during installation. Split pins are made from thick wire that has a half-circular cross section and comes in a variety of sizes and styles.

Any machinery is affected by vibration. Every bolt and nut must be protected from vibration. This problem can be solved in machinery with cotter pins.

What are Cotter Pins? Definition, Meaning

Using a cotter pin, the components are fixed in their place by passing through the hole. A cotter pin is a metal fastener used to attach two objects together. These pins are also known as split pins or cotter keys in the U.S. Cotter pins have a semicircular cross-section and are made of thick wire.

  • Axial motion along the shaft is usually stopped with these pins. The pins are wedge-shaped or tapered and driven into the holes.
  • Tapered refers to the fact that the pins compress as they enter the holes. During compression, friction is generated, which prevents the pin from loosening and ensures smooth operation.
  • Using a cotter pin, you can secure a component in a hole. Typically, cotter pins can be removed by pulling them out. Although cotter pins are all metal fasteners, they come in a variety of types.

How Does Cotter Pin Work?

Cotter pins or split pins work on locking mechanisms. A cotter pin prevents a bolt from being removed from the hole in which it is inserted. The use of a cotter pin is not supported by all bolts. Cotter pins can only be inserted into bolts that have holes. Cotter pins cannot be inserted without a hole.  A variety of applications can be performed with it. During installation, you need pliers, a castle nut, a drilled bolt, and pliers to make these fasteners.

The cotter pin can be used by simply putting it through the hole of the bolt. After twisting the prongs on the cotter pin, turn them outward and away from each other. In spite of people’s impression that cotter pins are best twisted together, these simple fasteners offer the greatest protection against loosening when twisted apart. When the cotter pin is used this way, it is less likely that the bolt might also emerge if the cotter pin wiggles out.

Specifications of Cotter Pin

  • In addition to being inexpensive and corrosive resistant, plastic is easy to mold, but only light loads should be molded in it.
  • A thin, malleable steel is somewhat weaker than other types of steel since it is more malleable.
  • The hardened steel version of steel is stronger, but it is also more brittle. In order to make it durable, it is heat-treated.
  • Despite its low magnetic permeability, brass is strong, conductive, and corrosion-resistant.

Types of Cotter pins 

The cotter pin is available in many different types today. R-clip pins and bowtie pins are two types of cotter pins that are used in different settings and are the most commonly used. It is even possible to find a cotter pin that is circular or rounded called a circle cotter. Although they all perform the same basic function, they differ depending on the type of machinery involved and the size of the components being connected.

It is common for cotter pins to have a slightly larger body in countries such as the United Kingdom. This allows the device to be wedged snugly between two components in order to hold them in place. In contrast to most United States cotter style pins, this body has a slightly larger diameter, but is especially useful for applications avoiding friction and slippage between components. In today’s globalized world, many corporations have become more international in scope, which can result in confusion, since cultures and settings have different interpretations of what constitutes cotter pins.

There are eleven major types of cotter pins:

  • Barrel Cotter Pins
  • Straight cotter Pins
  • Cotter Pin with a Key
  • Dipped Cotter Pins
  • Spring Cotter pins
  • R-pins or R- clips
  • Split Cotter Pins
  • Standard cotter Pins
  • Bow Tie Cotter Pins
  • Extended Prong Pins
  • Hammer Lock cotter Pins

Barrel Cotter Pins

There are two different ends on barrel cotter pins, one long side, and one short side, with a cylindrical shape. Threaded hoses and pipes can be connected using these pins via threaded joints. As an example, it can be used to connect two pipes or hoses.

Straight Cotter pins

In addition to looking like cylinders, straight cotter pins do not have rounded edges, but have one. There are straight ends on them. It does not have a curved or rounded end. Since these pins are straight, they are best for securing items that move frequently since they do not easily break off.

Cotter pin with a key

There is a “T” shaped design on the ends of these pins. As an added security measure, this cotter pin has holes in the wood as well as a key for increased security. Enough force applies when the pin is pulled out from the part.

Dipped cotter pin

This is a type of cotter pin that has two ends in which one of the ends in which one end has a head which is flat and has a hole and the second end has a T-like shape.

Cotter pins of this type are typically used for tightening dust caps around engine shafts with certain types of mandrels.

Using the dipped cotter pin, airtight seals are created between the capped-off area and any other components that come in contact with it (such as other components within the engine).

Spring cotter pin

An additional gripping power is provided by the spring cotter pin’s tension force. There is usually no alternative to this pin when applying pressure to an object is not possible. For example, pipes and hoses move or rotate without warning.

There is a “T” shaped end on the spring pin, which can be curved or straight depending on the installation. Surface area is generally required for larger diameter objects. Consequently, these objects have a straight design, but smaller diameters mean they have a smaller surface area, and they provide a good degree of curvature.

R clips or R pins

An R-pin, also known as a hairpin pin, is a sprung pin with a bent section balanced from a straight section to make a loop on the head.

The straight part of the R-pin passes through a hole in the shaft, and the bowed parts of the pin clamp on the outside of the shaft. To remove the pin from the hole, put your finger in the ring located on the pin’s head and drag it out.

Split-cotter pins

There are many types of cotter pins, but one of the most popular is the split cotter pin. The bulbous heads of these pins are constructed from a semicircular wire bent over a flat surface.

Split cotter pins are installed in predrilled parts and secured with deformable tines. Also, it acts as a brake for the clevis pin. There can only be one application per application. Each pin has a different design depending on how the wire bends and connects.

Standard cotter pin

It is possible to design these types of cotter pins in a curved or straight shape. It has a good grip when connected to other parts by hand because of its large surface. Following are the two different ends of the standard pin.

The pin is connected to the other pin by one end. In order to connect the pin to an object, the second end is used.

Bow tie cotter pins

The clip wire on bow tie pins is connected into a complete circuit, unlike hairpin clips or twist pins. It is possible to attach a clip to a shaft using a deformable wire break.

Extended Prong Pins

There are several types of cotter pins, but extended prongs are the most common. Unlike other cotter pins, extended prong cotter pins have two long and narrow prongs that are parallel to one another. There is a slight difference between one of the prongs and the other.

A cotter pin with extended prongs can be used by simply inserting it into a hole. Once the prongs are bent around the back of the component, you can attach them to the component. If the prongs of the cotter pin are bent, they will secure the component and, thus, the cotter pin itself.

Hammer Lock cotter Pins

As the name implies, hammer lock cotter pins require a hammer to install. The prongs on these pins resemble those on cotter pins. Cotter pins with a hammer lock have a curved end, unlike those without. Long prongs curved inward toward their opposite, shorter counterparts.

Hammer lock cotter pins can be used by inserting them into holes and striking them with hammers. The ends of the prongs close together when you hammer the head.

Cotter pins with extended prongs, R-clips and hammer locks are among the most common. The metal is bent into two prongs and consists of nothing more than a single piece. There are, however, differences between each type. It is necessary to bend extended prong cotter pins manually around the back of components. The curved prong of an R-clip cotter pin wraps around the side of the component. It is necessary to use a hammer to install a hammer lock cotter pin, which seals the prongs together after installation.

Parts & Construction of a Cotter Pin

The new cotter pin has an inner flat surface that touches its length. As a result, it looks like a split cylinder. In order for the pin to remain in its position, both edges of the pin flex, and the pin becomes firmly fixed. In the process of removing it, flex fatigue will occur; therefore, the pin needs to be discarded and replaced.

They are constructed of soft metal so you can easily install and remove them, but do not use them if shear forces are to be applied. The construction of cotter pins is made of aluminum, mild steel, stainless steel, bronze, or brass.

What Do You Know about Clevis Pins?

Clevis fasteners are two-part fastening systems consisting of a clevis pin and clevis. At the end of the prong, there is a hole in which clevis pins can be inserted.

There is a hole at the end of each prong along with a U-shaped design. Bolts are similar to these pins, but they have a cross-hole for splitting pins rather than threaded holes.

By using the clevis pins, the tang can be fixed in position within the clevis gap. Clevis and pins are just one of many types of shackles, but clevis and pins are not the only ones.

The straight shackle resembles the letter C, with two holes on each end; when the clevis pin is inserted, the clevis can rotate around the pin’s axis. Providing a loop at a right angle to a rotation axis, a twist shackle is a design that allows rotation to occur.

Clevis pins can be made from large bolts, but bolts are not designed to withstand the lateral stresses of clevis pins. Most farm trade clevis pins have larger heads and are safer to use for rigging.

The twist shackle is used to hitch older implements designed to be pulled by draft animals.

The purpose of a clevis pin is to prevent two pieces from moving in relation to each other, just as a set screw does. Due to the fact that holes must be drilled in both parts, a clevis pin is less adjustable. As a result of the low likelihood of clevis pins coming loose due to vibration, they are also more secure.

How are cotter pins and clevis pins different?

There are three parts to a clevis pin: a head, a shank, and a hole. At the opposite end of the pin from the head, the hole passes through the shank. After assembly of the parts to be fastened, a cotter pin is inserted through the hole to hold the clevis pin in place

What do you know about spring pins?

A roll pin or spring pin is designed to be inserted into a hole that is smaller than the pin’s diameter. When installed, the pin is sprung so that it can decrease in diameter, ensuring a tight fit while exerting a retaining force against the hole walls.

In order to expand to its resting diameter, a pin exerts a force against its sides when compressed into a hole. As a result of this force, friction is created in the hole, which maintains the pin’s secure position.

An outer diameter of the spring pin is formed by curving a thin sheet of material. In most cases, they are formed from sheet steel and have chamfers at each end, making them easy to push into holes.

These pins can be inserted through shafts perpendicular to their axis to hold components onto shafts. It is necessary to use a pin that is longer than the diameter of the shaft in this case. By inserting these pins through concentric holes in two or more components, they can also be used to join two or more components together.

There are two varieties of spring pins which are

  • Coiled pins
  • Slotted pins

Installation: A Guide to Installing Cotter Pins

Now you already know that cotter pins have a lot of variety of uses. You can do mechanical work and also use cotter pins for a lot of basic stuff as well.

For Example, Cotter pins can be used to make puppets with moving parts, statement necklaces, knitting looms, and garden pinwheels. Whenever you need something larger, stronger, and weather-resistant than hairpins, this can be used. The use of cotter pins on trailer hitches is common as well. Designed for heavy-duty use, these hairpin cotter pins are zinc plated, corrosion-resistant, and stable.

Cotter pins are used to secure bolts by sliding them through slotted nuts. Once you have reached the end of the loop, pull it through. You can then grab the split end with pliers. Ensure it is locked around the castle nuts by bending it in a locked position.

You must not use a single cotter pin more than once. If a cotter pin is used more than a single time then it is possible to weaken the metal or break off a cotter pin after using it again.

In the following part we are going to discuss about the proper process in order to install a cotter pin.

Select the correct size of cotter pin

It is important to select the right cotter pin size. The cotter pin size can be determined by purchasing a cotter pin kit.

You should place your cotter pin on top of the castellated nut to determine the size of the cotter pin. You know you have got the right size if it fits in the grooves without being too big or small.

Drilling a hole into the bolt (Additional Step)

A slotted nut can usually be installed in a bolt with a hole already there. When the cotter pin is installed, it will be ready to be used.

However, there are times when the bolt and nut connection must be secured by drilling a hole.

You should choose a drill head that is a bit smaller than your cotter pin. A drill head with a 3/16th hole is used for a 1/8th cotter pin, for instance.

In this case, the bolt will be holed near its end while leaving a section of threads at its end.

Make sure the drill is level in order for it to travel straight across. You can add some extra lubrication which could help you drill the metal against metal.

Coater pins should be inserted in bolt holes

In the hole of the bolt, insert the split end of the cotter pin. The pin must not too snug or too loose should be the feeling when you put it on. The cotter pin loop should be touched by the looped end of the cotter pin before it is inserted through the hole.

Split the cotter pin ends and bend them

In order to finish the castellated nut installation, the cotter pin needs to be secured around it. Grab the split end of the split end and bend it around the castle nut using pliers. The other end should be done in the same manner.

After the ends have been squeezed and split, use the pliers to ensure that they are securely connected to the nut and bolt.

A single, simple motion is necessary when bending the legs. They might break off if you fiddle with them too much. New cotter pins should be used instead of old ones, since they should only be used once.

With the cotter pin installed, the castellated nut will not become loose once the bolt has been tightened. It is important to follow this process in order to install a cotter pin properly and at the correct location.

To ensure the safety of those working with cotter pins, they should be familiar with their usage.

Steps to Install a Hairpin Cotter Pin?

In trailer hitches, hairpin cotter pins are used as hitch pin locks. It is important to use hairpin cotter pins on the hitch in order to ensure that it is properly and securely secured. The hairpin cotter pin is also known as the R-pin because it looks like an R shape.

Properly installing the hairpin cotter pin allows the trailer to stay attached to your vehicle without dislodging. Ensure that the pin hole is aligned with the hitch. The bendy end of the pin should be facing down when installing it

Once that is done, make sure the hole on the hitch pin is straight up and down. It is important to inspect the hairpin cotter pin, which is also known as a hairpin clip. It is important to check that the bend at the bottom of the hairpin clip is touching the straight end of the clip. As a result, the hairpin clip will securely attach to the hairpin.

Insert the straight end into the hole on the hairpin cotter pin while holding the cotter pin in your hand. For the hitch pin to slide in, you may have to turn it. Because of the springy design of the hairpin clip, it should be difficult to slide in.

After you have installed the system, inspect it. Verify that the bend at the end of the straight line touches the end of the bend. Using a larger size hairpin clip is necessary if there is a gap.

How can you use a Cotter Pin?

It is particularly important for heavy machinery, such as cars and trailers, to have cotter pins that help prevent nuts from sliding off bolts. When castellated nuts are installed, or other types of hitch pins are installed, cotter pins are inserted near the end section of the bolt.

By creating a lock on the bolt’s end, the split pin prevents the nuts and bolts from falling off due to vibrations from the vehicle. As a result, parts can fall off machines, causing accidents.

It may be necessary to drill a hole in the bolt if one does not already exist. You should chose a drill bit that is slightly larger than the size of the cotter pin.

This metal drilling can be improved with the use of lubricant. Bolt holes are secured by the bulbous end of cotter pins. The split end of the cotter pin should be bent with pliers. The castle nut should be wrapped around each end.

To keep the bolt and nut on the machine securely together, this locks them together.

The hairpin cotter pin is another type of cotter pin used as a trailer hitch component. In order to create a secure, stable hold, these hairpin clips are inserted into the trailer hitch pin.

You can also use split pins to make puppets’ moving parts as part of a DIY project. In addition to forming pinwheels for your yard, making statement necklaces, and creating knitting looms with split pins and cans, you can also make pinwheels using split pins.

Hairpin cotter pins have only one plain pin out of two, so you can only insert them from one side. The pins are bent according to the need in opposite directions after they are inserted into the bolt hole. The extra length of the pin should then be bent with pliers.

Cotter Pin Bending Tool: What is it?

As a tool for bending cotter pins, you can use pliers. The split ends of the cotter pin can be separated with pliers after the cotter pin has been inserted into the bolt hole.

The split ends can then be wrapped around the castellated nut with the pliers. Complete the installation of the cotter pin by ensuring the ends sit flush.

By having a set of pliers, you can choose the right one for the job you are doing.

What Is the Best Way to Measure Cotter Pins?

There are two measurements that matter when installing cotter pins. It is important to know the diameter and the length of the cotter pin before choosing the right one.

When determining the length of a cotter pin, measure from the end of the short side to the base of the rounded portion.

Measuring both pins together will give you the diameter of the cotter pin. It is not necessary for the hole to be bigger than the eye, as the rounded portion is not supposed to fit through the hole.

What are split pins and how it is different from cotter pins?

Parts can be held in place with a split pin, which is generally made from soft, malleable metal. There is a pronounced loop at the closed end of the split pin, which is typically made as a flat, round, or half-round pin bent twice.

When the pin inserts into a hole, its diameter compresses due to the spring action. In the insertion process, a force is applied to the hole, retaining the pin. It is often referred to as a self-locking fastener used in double shear applications that spring pins are designed to lock in place.

Both cotter pins and split pins both same a similar nature of mechanism, but there are some noticeable differences.

In general, cotter pins are made of mild steel and are used to lock nuts in place. In order to prevent the nut from falling out of the bolt, they are inserted into the hole and then bent into a variety of shapes. In contrast, split pins are made of a harder grade of steel.

Split pins are also known as roll pins. There are two edges almost touching each other on a piece of flat spring steel. It is held in place by the spring tension in a hole when it is forced into it.

In technical terms, a cotter pin is a wire length that is folded nearly in half and has an open eye on the folded half. It is easier to secure the cut ends because they are staggered. To prevent a fitting from turning, the end of the cotter pin is bent back over the fitting.

It also depends on where you live. For example, in the United States, both pins are seen as identical. One might be found on a car axle to hold a castle nut. When it comes to bicycle pedal cranks, cotters (or cotter pins) are normally used in the UK to hold cranks on shafts.

Frequently Asked Questions (FAQs) on Cotter Pin

Can cotter pins be reused?

Split pins can be made of a variety of materials that can be bent sufficiently.  Deformed pins generally retain strength and provide a reliable and powerful locking system once they are deformed.
It is generally not possible to reuse cotter pins. It is because when the pins bend, it weakens them. In this case, the pin may fail, and the nut may start spinning loosely as a result.

For what purpose do Cotter Pins serve?

Coater pins are fasteners used to secure nuts to screws. In order for a pin to be used, a small hole needs to be drilled in the bolt.

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