Cotter Pin!? What the heck is that?

Welcome back to the next installment of our “what the heck is that” series, where we discuss some of the unique fasteners and electronic hardware that manufacturers use in the design and assembly of their products. This week, we are introducing you to our friend, the Cotter Pin!

Cotter Pins, AKA Split Pins, R Clips or R Pins, Hitch Pins or Hitch Clips, Safety Pins, Circle Cotters, Retaining Pins or Locking Pins, may not be the most renowned piece of hardware, yet they have been quietly holding together our world in more ways than you might imagine. For starters, these pins are non-threaded fasteners, which means that they do not have the risk of loosening due to vibrations as is the case in some screw or bolt connections. Furthermore, Cotter Pins are easy to install/remove and are inexpensive to produce—making them valuable & cost-effective components that guarantee the stability and functioning efficiency of numerous mechanisms across a variety of industries. Keep reading to learn more about these pins and to see if they would be a great fit for your next big project.

What are Cotter Pins?

Cotter Pins are double-structured pins crafted from semi-round wires, that have a loop on one end that serves as a head. The completed component showcases one wire end extending past the other, ending with a chisel-like point.

At the most basic, cotter pins are fasteners that are used to secure various assemblies in place. Typically, they are shaped like a “T” or an “R”, and are inserted into holes that run through the parts to be connected. They are then split into two prongs at the opposite ends, which are then bent to prevent the pins from slipping out and to securely hold the assemblies together.

One key advantage of cotter pins is their inherent simplicity. With their straightforward design, they can be easily installed and detached without the necessity for any specific tools. Furthermore, they offer robust links that prevent the secured pieces from becoming loose or disassembled. When used with castle or slotted nuts, they become a safety locking device.

Another important benefit offered by cotter pins is their ease of removal, which enables swift disassembly or maintenance tasks. When the need arises to dismantle/disassemble components, cotter pins can be easily taken out by straightening or bending back their split ends to their original position. This feature simplifies repair or maintenance operations.

Cotter pins also allow for a certain degree of motion (pivot) depending on how they are installed. This is beneficial in applications like bicycle crank arms where you want the crank to remain secure while also allowing it to rotate.

Who uses Cotter Pins?

Cotter Pins are widely used across a range of industries due to their simplicity, reliability, and versatility. The following are some primary industries where cotter pins are frequently employed:

  • Aerospace Industry: Cotter Pins play a vital role in the aerospace industry, where safety and reliability are paramount. They are used to secure critical components such as landing gear, engine parts, and control linkages, ensuring that they remain in position during flight. For example, control linkages encompass control surfaces such as ailerons, elevators, and rudder, as well as the cockpit controls, all of which have numerous pivot points requiring both security and mobility. Cotter Pins are perfectly suited for these uses.
  • Automotive Industry: In the automotive industry, cotter pins are utilized in various components, particularly in suspension systems, steering linkages, transmission linkages, wheel assembly, brake system, etc. They secure ball joints, tie rod ends, and other critical parts to ensure safe and reliable vehicle operation.
  • Agriculture Industry: In the agricultural sector, cotter pins serve the purpose of fastening elements in various farming machinery, including plows, harrows, and cultivators. Cotter pins also find use in several components of tractors, including anchoring the joint connections in the steering mechanism, maintaining components in the transmission system, and fastening parts in the hydraulic systems.
  • Marine Industry: Within the marine industry, Cotter Pins are widely employed to secure clevis pins, turnbuckles, and various fittings in rigging systems and boat hardware. For instance, within marine engines, cotter pins are often used to secure various components and assemblies, such as linkages, connections, and valves. Offering a swift and secure fastening solution, these pins demonstrate reliability even in corrosive marine environments.
  • Military and Defense: In the military and defense industries, cotter pins are used to fasten components in weapons, vehicles, aircrafts, naval assets, and communication equipment. In addition, Cotter Pins are deployed in a wide array of other portable gear and systems utilized by military personnel in operational settings. These can encompass everything from temporary bridges and fortification structures.

Other industries that make use of Cotter Pins are: the Industrial and Machinery Industry, where Cotter Pins are used for securing components, such as pulleys, gears, and levers; the Mechanical and Electrical Engineering Industry, where they are used to to fasten parts, such as bolts, nuts, and shafts; the Recreational and Sports Equipment Industry, where they secure various moving parts and components found in recreational equipment, such as bicycles, motorcycles, and sports gear; the Construction and Heavy Equipment Industry, where these pins are used for various applications, including securing hitch pins, linkages, and hydraulic connections; and the Furniture and Manufacturing Industry, where these pins are utilized to secure joints, hinges, and other components in conveyor systems, furniture assembly, and .

What standards, materials and sizes are available?

Materials: Cotter pins can be manufactured from different materials like steel, stainless steel, brass, and aluminum. Steel cotter pins are often enhanced with a zinc coating for added resistance to corrosion. Stainless steel pins are favored for their superior strength and corrosion resistance, particularly in harsh environments.

Sizes: Cotter pins come in a spectrum of sizes, generally ranging from 1/32″ to 3/4″ in diameter and 1/2″ to 6″ in length. The appropriate size is dictated by the application and the dimensions of the hole where the pin will be placed.

Standards: Various nations and regions adopt their own standards for cotter pins. Some of the most frequently used ones include the American Society of Mechanical Engineers (ASME), American National Standards Institute (ANSI), British Standards (BS), Military Specification (Mil-Spec) Standard, and the Deutsches Institut für Normung (DIN).

Commercial Standards include: ASME B18.8.1

Mil-Spec standards include: MS9245

Are there other factors to consider?

YES!! The efficacy of cotter pins are greatly influenced by their proper installation and maintenance. The following list has crucial points to keep in mind.

  • Selection: Opt for cotter pins that fit into the hole securely without being overly tight. The length should be sufficient for the prongs to be bent appropriately without leaving excessive overhang.
  • Installation: During installation, ensure the prongs are split and bent sufficiently to secure the pins. Tools like pliers or a cotter pin puller can aid in the process of installation and removal.
  • Inspection: Regular checks on cotter pins are crucial, particularly in applications under high-stress or where safety is paramount. Look out for signs of wear, corrosion, or distortion, indicating potential need for replacement.
  • Replacement: When extracting cotter pins, it’s typically advised to substitute them with new ones, as the bending and straightening process can fatigue the metal, undermining their strength.

Cotter Pins at MF Supply

We currently offer:

  • A full range of commercial parts, including parts that are ROHS compliant.
  • Inch Cotter Pins are now available for online purchase at our website! Stock sizes include 1/16 through 1/2 in Steel with a Chisel Point and Zinc Plating, as per standard ASME B18.8.1 specifications.
  • Mil-spec Cotter Pins MS9245 are also available for online purchase. Stock sizes include 1/32 through 5/32 in T321 Stainless Steel , with Manufacturers Certifications.
  • Please send a Request for Quote for any other Cotter Pin not listed on our website.
  • Brand names and generic equivalents.
  • Custom made parts per print.

For more detailed information on Cotter Pins or other products, visit us at our website or Request a Quote today, and our MF Supply team of sourcing experts can help you find what you need. Finding the right screw for you” is our tag line after all!

Book a one-on-one consultation with our President, Robin, to discuss how MF Supply can help you solve your Industrial Sourcing, Fastener, and Safety concerns.

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MF Supply is a WBE/WOSB certified supply chain partner to business, industry and government.  We are sourcing experts and stocking distributors of Hardware, Precision & Mil-Spec Fasteners and Safety supplies.  For more than 50 years, we have been supplying manufacturers in the electronics, industrial, commercial, aerospace and military markets with the full range of fastener products and services.  Our Cage Code is 58QG4 and our registered name is RL Supply Inc dba MF Supply.