What Are Cotter Pins?
Cotter pins are among the most commonly used fasteners in various applications across many different industries, especially those relying on mechanical engineering. They’re incredibly simple yet highly effective devices that play a vital role in securing components in place and preventing their unfastening due to vibration or other external forces. This article will discuss what cotter pins are, how they are used, how they’re classified, and what materials they’re made of.
What Are Cotter Pins Used For?
Cotter pins, often referred to as split pins or cotter keys, are common locking pins that secure other fasteners or bolts in place. They’re particularly useful in high-stress applications where other fasteners might be subjected to immense stress and/or vibration.
However, some lighter applications that don’t produce high-stress loads and excessive vibrations rely on cotter pins as fastening elements themselves, which attests to their versatility. There’s a vast application of cotter pins in different industries, especially automotive, aerospace, and maritime industries.
Depending on the application and loads, cotter pins are made of different materials. This includes zinc-plated high-carbon steel, mild steel, and stainless steel, but also softer metals as well, such as copper or brass.
How Do Cotter Pins Work?
All cotter pins share the same working principle: they pass through a through-hole in a fastener, such as a bolt or a threaded rod, thus preventing a hex nut or a castle nut from coming off. However, there are some variations in how each type of cotter pin is secured.
For example, a typical split pin is made of a soft metal (of varying thickness) that’s bent in the middle once the pin has been passed through the hole. The bent ends of the cotter pin, referred to as prongs or tines, form a U shape with an o-loop at the other end. Once they’re fitted through a pre-drilled hole in a mechanical element, the tines are bent back using pliers to secure the cotter and prevent it from coming out.
R-clips, also known as R-pins or hairpin cotter pins, work on a similar principle. However, since they’re designed differently (one prong is straight, and the other one has a semi-circular shape), they’re secured differently.
The straight prong of this metal fastener goes through the cross-section hole of a shaft, while the circular one conforms to the shaft’s rounded edge. Since they’re made of harder, springier steel, the pressure exerted by the tines upon the shaft secures the pin in place.
A Rue ring cotter is a combination of the two previously mentioned types. While one prong goes through the through-hole, the circular shape of the other prong slides over the circumference of the shaft, securing the pin in place. You can additionally bend each prong to prevent any accidental release.
Cotter Pin Applications
The automotive industry is one of the most common applications of cotter pins. These pins, especially corrosion-resistant stainless steel cotter pins, are typically used to secure castle nuts on ball joints, tie rod ends, and other suspension components that are susceptible to vibration.
Airplanes are also subject to extreme vibrations and stress, so it’s vital to ensure that all mechanical components and elements are fastened securely. Control surfaces, engine components, and landing gear assemblies in the aerospace industry all rely on cotter pins for fastener security.
The same applies to marine engines, in which cotter pins are used to secure a number of nuts and bolts on the engine and other components exposed to water and salt. This is where corrosion-resistant material options come into play, as water and salt can cause corrosion.
Cotter Pin Materials
Depending on the application, cotter pins can be made from a variety of different materials. The most commonly used options are stainless steel and zinc, but other options are also available.
One of the most commonly used materials is stainless steel, primarily for its durability and corrosion resistance. Cotter pins made of this material are typically exposed to harsh environments, such as salty seawater. Stainless steel pins are also more resistant to heat, which makes them more suitable for high-temperature applications.
Zinc-plated high-carbon and mild steels are the most economical options, mostly used in applications that don’t expose the pin to harsh environments or high thermals. Zinc-plated cotter pins may lack the durability of stainless steel, but they’re still very effective at keeping things in place.
Cotter Pin Types
Cotter pins come in a variety of shapes and sizes, and some of the most commonly used types include:
- Prong Cotter Pin — Best known as split pins, which are inserted in pre-drilled holes, and their prongs bent backward.
- Hairpin Cotter Pin — Also known as R-clip or hitch pins, these pins are easily removable for less demanding applications.
- Rue Ring Cotter Pin — This type is among the easiest to remove self-locking cotter pins, which have a manually triggered lock that is lifted away from the bolt with minimal force.
- SLIC Pins — This is basically a clevis pin with an integrated cotter pin functioning as a quick-locking pin.
- Bow-tie Locking Cotter Pin — A self-locking variation of an R-clip.
- Taper Pin — These are mostly used to prevent axial movement along the rotating shaft. Their shape means they’re compressed when driven into a hole, which causes friction and prevents unfastening.
Cotter Pin Sizes
Besides coming in various shapes, cotter pins also come in different sizes to accommodate different applications. The size of the pin is determined based on the size of a through-hole it passes through. The most common cotter pin sizes are 1/16”, 3/32”, 1/8”, 5/32”, and 3/16”.
Buy Cotter Pins
Despite their simplistic design, cotter pins are highly effective fasteners that play a crucial role in securing various mechanical components in place across various industries. If you want to learn more about cotter pins and other types of fasteners, check out our extensive download library filled with professional literature about fasteners and other industrial parts.