What is a Cotter Pin? | How does a Split Pin work?

What is a Cotter Pin?

A cotter pin is a wedge or pin that passes via a hole to fix the different components in their place. In the USA, the cotter pin is also known as a split pin or cotter key. The cotter or split pin is made of thick wire with a semicircular cross-section.

Cotter Pin

These pins are available in different designs and sizes. The term “split pin” uses for the “crank cotter pin,” which uses for locking the bicycle pedal crank with the bottom bracket axle.

In most cases, these pins use to stop axial motion along the shaft. They are tapered or wedge pins that are driven into the holes.

The term tapered represents that the pins compress as they enter the holes. When the pin compresses, it generates friction which prevents the pin from loosening and helps to work smoothly.

Working of Split Pin

The cotter or split pin works on the locking mechanism. It can use for a variety of applications. They are easy-to-use fasteners that only require a drilled bolt (a drill is required if the bolt doesn’t have a hole), pliers, and a castle nut.

Types of Cotter Pins

The cotter pin has the following major types:

  1. Split cotter pins 
  2. R-pins or R-clips
  3. Standard Cotter Pin
  4. Spring Cotter Pin
  5. Barrel Cotter Pin
  6. Dipped Cotter Pin
  7. Straight Cotter Pins
  8. Cotter Pin with a Key

1) Split Cotter Pins 

The split cotter pin is one of the most popular types of cotter pin. These types of pins are constructed of semicircular wire, which is bent over the flat side to make bulbous heads.

Split cotter pin The split cotter pin installs in pre-drilled parts and secured with a deformable tine. It also uses as a brake for the clevis pin. It can be only one-time for applications. These pins are available in a variety of individual designs depending on the wire bend and connection of the wire.

Read More: Different types of Engines

2) R-pins or R-clips

They are also known as hairpin pins. The R-pin is a sprung pin that has a straight section. This section is bent to make a ring or loop on the head, with a bent section balanced from the straight pin.

R pin

The curved part is clamped on the outside of the shaft, and the straight part or section pushes to go into the shaft via a hole that holds the pin in place. You can also insert your finger in the ring located on the head and drag the pin out of the hole.

3) Standard Cotter Pin

These types of cotter pins may have curved or straight designs. Due to its large surface, it has a good grip when connecting to other parts through the hand. The standard pin has following two different ends.

  1. One end uses to connect the pin with the other pin.
  2. The second end uses to connect the pin with an object.

Standard Cotter Pin

4) Spring Cotter Pin

The spring cotter pin has a spring that helps to produce tension force for extra gripping power. This pin generally uses for conditions when no other option is available to apply the required pressure on the object (e.g., on hoses and pipes, which often rotate or move without warning).

Spring Cotter Pin

The spring pin has a “T” shaped end, which may be curved or straight depending on the installation. Larger diameter objects generally need more surface area. Therefore, such objects use a straight design, but smaller diameters result in less surface area and provide well curvature around the object.

Read Also: Working and Construction of Camshaft 

5) Barrel Cotter Pin

The barrel cotter pin has the same looking like a cylinder with rounded sides and two different ends (i.e., one short side and one long side). This type of pin uses for threaded joints (for example, it uses to connect two hoses or pipes together).

6) Dipped Cotter Pin

The dripped cotter pin has two ends:

  1. One end has a flat head with a hole.
  2. The other end has a “T” shape.

These types of cotter pins are most commonly utilized to ensure the tightening of the dust cap to a mandrel that fits around the shaft of the engine.

After the installation of the dipped cotter pin, it makes airtight seals between the capped-off area and other parts when they make contact with each other (such as other internal components of the engine).

7) Straight Cotter Pins

The straight cotter pins are looked as cylinders that haven’t any round edge. They have straight ends. There is no curved or rounded end. Because of their straight design, these types of pins are best for securing frequently moving objects as they don’t come off the objects easily.

Straight Cotter Pins

8) Cotter Pin with a Key

The ends of these pins have “T” shaped designs. This cotter pin also has an additional key to increase security, e.g., holes in the wood (this pin is pulled out before leaving if adequate force is still applied).

Construction and Parts of Cotter Pin

The inner flat surface of the new cotter pin touches to its length; due to that, it looks like a split cylinder. As it is inserted, both edges of the pin flex and fix the pin into its position. As it removes, there will be an occurrence of flex fatigue; due to that, you will need to discard and replace the pin. 

Soft metal is used for the construction of these pins so that the installation and removal of the pins can be easy, but it is not recommended that you use them to withstand strong shear forces. Material such as aluminum, mild steel, stainless steel, bronze, or brass is used for the construction of split pins.

What is a clevis pin?

clevis fastener is a two-part fastening system that has a clevis pin and a clevis. This clevis has a U-shaped design with a hole at the prongs’ end so that the clevis pin can move in it. These pins are similar to bolts but are moderately unthreaded or threaded with the cross-holes for split pins. 

The tang is mounted in the clevis gap and can be fixed in position by the clevis pins. A simple pin and clevis combination is often referred to as a shackle, but clevis and pin are just one of many possible forms of the shackle.

clevis pin

These pins are used in marine equipment and agricultural machinery and in a variety of fasteners in the aerospace, locomotive, and construction industries. The clevis pin also uses to connect the control surface and other parts with the servo controls on airworthy model aircraft.

As part of the fastener, the clevis permits the ability to allow some axes to rotate and limit other axes’ rotation.

The bolt may also use as a clevis pin, but the bolt cannot withstand the lateral load that the clevis pin can withstand. 

The clevis pin must fit closely into the clevis hole to decrease the wear and the damage or failure rate of the pin or clevis.

FAQ Section


Is Cotter Pin reusable?

The split pins may be constructed from different types of materials that can be bent adequately.  In general, once the pin is deformed, it will retain its strength and deliver a reliable and powerful locking mechanism.

Generally, the cotter pins can’t be used again. This is because the pins weaken as they bend. This may cause the pin failure, and the nut starts to spin loosely.

How to remove a Cotter Pin?

The procedure of the cotter pin removal is very easy. First of all, you need to get pliers and use them to bend the pin arms and make them straight so that the pin can easily pass through the hole.

In the case of worn pins, these arms may damage, and you can easily remove and replace the rounded eye section with new ones.

What is a Spring Pin?

Spring pins are a type of fasteners used to fix the relative position of more than one part of a machine. A slotted spring pin is a cylindrical pin that is wound from strips of slotted material, which gives the pin some flexibility during the insertion process. This pin is also known as a roll pin. The spring pin has a larger body diameter than the hole diameter.

Due to the spring action of the pin, the pin diameter compresses when it inserts into the hole. The pin applies a force on the hole during the insertion process, which holds the pin in position. Spring pins are considered self-locking fasteners designed for double shear applications.

Why should you use a Cotter Pin?

The cotter pins are used in a wide variety of applications. It can be used as a quick locking mechanism that can easily disassemble and replace, but its main advantage is that it prevents the nut from loosening due to vibration.

There are a variety of lock nuts that can be installed quickly, but depending on the strength of the vibration, they will all loosen over time. Split pins completely preclude the possibility of the nut loosening if the force on the nut is great abundant to sever the pin.

What are Cotter Pins Used for?

A cotter pin is a fastener that secures a nut to a screw. To use a pin, you need to drill a small hole in the bolt.

Read More
  1. Different types of Engines
  2. Types of Pumps
  3. Different types of Compressors
  4. Working of Crankshaft

2 thoughts on “What is a Cotter Pin? | How does a Split Pin work?”

  1. HI,
    1.Cotter Pin, Hairpin, Hammerlock, Steel, Spring Steel, Zinc Plated, 6 mm Pin Dia x 100mm -24 nos


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