Cotter Pin!? What the heck is that?
Posted: August 1, 2023 | Author: mfsupplyblog | Filed under: Circle Cotters, Cotter Pin, Fasteners, Hair Pin Clip, Hitch Clips, Inch, Locking Pins, Metric, Mil-Spec, Pins, R Clips, R Pins, Retaining Rings, Safety Pins, Split Pins | Tags: ASME B18.8.1, Bulk Pins, Circle Cotters, Cotter Pins, cotter pins for manufacturers, Fasteners, Functional Equivalent Pins, Hardware, Heavy Duty Fasteners, Hitch Pins, Inch Cotter Pins, Locking Pins, Mechanical Fasteners, Metal, Metric Cotter Pins, Mil-spec Cotter Pins, MS9245, Pins, Pins for manufacturers, R Clips, R Pins, Safety Pins, Split Pins | Leave a commentWelcome 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.
Six Reasons To Buy From MF Supply
- Full eCommerce Enabled Website With Technical Manual Available 24/7 – Visit our website and Create a New Account, track online orders, browse our product catalog, check technical specs, subscribe to our blog, or buy online. We are adding items and improving functionality daily!
- Same Day Shipping From The USA – Our hardware products are in stock and ship to you directly from our USA based distribution centers.
- Functional Equivalents To Expensive Brand Names- We stock and source alternatives to brand name fasteners, reducing long lead times and saving you money.
- Creatively Solve Problems – We are sourcing experts, offer competitive pricing and specialize in finding hard to find parts and reducing long deliveries.
- One-Stop Shopping On Certified Hardware – We stock and source a full line of fasteners including Mil-Spec, DFARS compliant and other industrial products.
- WBE/WOSB Woman Owned Certified Small Business – To meet your diversity & set-aside needs.
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.
Over 1.5K Dowel Pins, Cotter Pins, Spring Pins, and more Now in Stock!
Posted: July 7, 2023 | Author: mfsupplyblog | Filed under: Coiled Spring Pin, Cotter Pin, dowel pin, Fasteners, Hair Pin Clip, Hitch Pin Clip, Inch, Metric, Metric Dowel Pins, Pins, PRECISION DOWEL PIN, Slotted Spring Pin | Tags: Coiled Spring Pins, Cotter Pins, Dowel Pin, Fasteners, Functional Equivalent Pins, Hair Pin Clips, Hardware, Hitch Pin Clips, Mechanical Fasteners, Metal, Pins for manufacturers, Precision Dowel Pin, Slotted Spring Pins, Spring Pins | Leave a comment
Are you looking for Precision Dowel Pins, Cotter Pins, Spring Pins or Hair/Hitch Pin Clips?
If you are in need of any specific type of pins or clips for your next big project, you have arrived at the right place!
MF Supply is a WBE/WOSB woman owned business, and a trusted supplier of Functional Equivalent Pins & Clips to OEMs, Manufacturers, Industry, and Government. We offer a wide selection of over 1,500 inch, metric & Mil-Spec Pins, in Alloy Steel, Steel, and Stainless Steel materials, that are perfect for a myriad of applications. You’ll find in stock Pins in many sizes including major brands and equivalents to Blue Devil, Pic Design, WM Berg, Misumi and Unicorp; so you can choose the ones that best suit your needs.
Who uses Pins & Clips?
Pins & clips are commonly used on many industries, such as automotive, aerospace, electronic, machinery, tooling, agriculture, construction and many more where reliable and convenient fastening is a must. Continue reading to learn more about the characteristics of each pin or clip currently on our website, and how they could be of use on your next project.
Coiled Spring Pins: Coiled Spring Pins, also known as Spiral Pins or Coiled Pins, are headless, hollow pins with chamfered ends, made by shaping or wrapping a steel sheet into a slightly larger diameter than the standard size. Unlike the slotted pins variety, these pins are distinguished by their multiple walls.

Uses: These pins are frequently used to join and fasten two or more components together. When the pins are inserted into pre-drilled holes, their spiral shape allows them to expand and exert radial pressure against the sides of the hole. This creates a secure and snug fit/connection. Apart from their fastening functionalities, Coiled Spring Pins can also serve as effective retaining features. They have the ability to secure various items, such as gears, pulleys, or bearings, onto shafts, effectively preventing axial movement or slippage. Moreover, these pins can be utilized to accurately position and retain other components, ensuring precise alignment and preventing undesired movement.
Cotter Pins: Cotter Pins, also known as Split Pins, are double bodied pins formed from half-round wire, a loop at one end of which provides a head. The finished part has one end of the wire extending beyond the other end, with a chiseled point.

Uses: These pins are used to anchor various assemblies by inserting them into a drilled hole in the shaft or pin and spreading the points to hold the assembly in position. When used with castle or slotted nuts, it becomes a safety locking device. An 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 readily taken out by straightening or bending back the split end to its original position. This feature simplifies repair or maintenance operations.
Precision Dowel Pins: These pins are solid headless straight pins with a closely controlled diameter. Applications include a wide variety of uses, such as plug gage, hinge, or shaft. They are typically cylindrical in shape and made from materials such as hardened steel, stainless steel, or aluminum.

Uses: Precision Dowel Pins are widely utilized to achieve precise alignment and positioning of components. These pins undergo meticulous machining processes and are manufactured with strict tolerances to guarantee a snug and accurate fit. Precise tolerances of Dowel Pins make them excellent for achieving proper alignment of parts in high-speed assemblies, or as roller bearings in bus/truck wheel housings. By inserting them into corresponding holes in two or more parts, the dowel pins guarantee proper alignment and positioning of the parts in relation to one another. These dowel pins serve as reference points or datums, ensuring accuracy and precision throughout the assembly process.
Slotted Spring Pins: Sometimes referred to as Roll Pins, Expansion Pins, C-Pins or Tension Pins, Slotted Spring Pins are hollow, headless pins, slit longitudinally, having controlled lengths with chamfered ends, formed to a diameter somewhat greater than that of the hole into which they are to be assembled. These pins are cylindrical in shape and are able to compress and expand upon insertion into a hole. Additionally, they are commonly crafted from materials such as carbon steel or stainless steel.

Uses: Slotted spring pins are used for the purpose of securing and fastening components together. The slots present in the pin allow for compression during insertion and radial expansion, which generates outward pressure against the walls of the pre-drilled hole. This inherent self-retaining characteristic guarantees the pin’s retention and delivers a secure method of fastening. Spring pins are economical because they can simplify product design by replacing more expensive fasteners such as taper pins, set screws and straight pins. Stainless steel Spring Pins are commonly used in electronics and food industries.
Hair/Hitch Pin Clips: Hitch Pin Clips, also known as Hair Pin Clips, Bridge Pins or R-Clips, are double-bodied pins formed from round wires. These pins are formed in a way where one end is bent approximately 180° so that the two resulting sides meet or come close to meeting. The final pins have one side that remains straight, while the opposite side has one or more turns permanently formed into it.

Uses: Hair/Hitch Pin Clips are designed to serve as a mating part to several other pins. They provide a hassle-free way to attach and detach components without the need for additional tools or complicated fastening mechanisms. Hitch Pin Clips also act as a safety feature, ensuring that the connected components remain intact during operation. When the need arises to remove or replace a pin, Hitch Pin Clips present a simple and time-saving solution. By simply compressing the curved end and sliding it out of the hole, the clip can be easily removed. Hence, this allows for quick disassembly, maintenance, or component replacement without the requirement of specialized tools or lengthy procedures.
In-Stock Pins & Clips at MF Supply
We currently have in stock over 1,500 Pins & Clips in inch, metric & Mil-Spec sizes. The most common material options available are: alloy steel with bright or ebony black oxide finishes; steel with thermal black, mechanical zinc, zinc, and zinc phosphate finishes; and passivated stainless steel—including series A2, T321, 18-8, 300, 303, 316, 400 416, & 420.
Browse through the links provided below to find the Pins or Clips that you need, and that are currently available on our website.
- Inch Coiled Spring Pins: Stock sizes include 1/16 to 3/8 in Steel with a Thermal Black finish, and in 420 Stainless Steel.
- Inch Cotter Pins: Stock sizes include 1/16 to 1/2 in Steel with a Chisel Point and Zinc Plating, as per standard ASME B18.8.1 specifications.
- Mil-Spec MS9245 Cotter Pins: Stock sizes include 1/32 through 5/32 in T321 Stainless Steel.
- Inch Precision Dowel Pins: Interference / Press Fit & Slip Fit Dowel Pins in 300 Series Stainless Steel; Dowel Pins in 316 Series Stainless Steel; and Dowel Pins in Alloy Steel with Bright or Ebony Black Oxide finishes.
- Metric Precision Dowel Pins: Stock sizes include M1 through M10 diameters in 18-8, 300, 303, A2 Series Stainless Steel; and M2 through M10 diameters in 416 Stainless Steel.
- Mil-Spec Precision Dowel Pins: MS16555-1 through MS16555-145, MS16555-301 through MS16555-444 & MS16555-601 through MS16555-744, including between-spec sizes; and Mil-P-21143 Series in 303 Stainless Steel.
- Inch Slotted Spring Pins: Stock sizes include 1/16 to 1/2 in Steel wth a Thermal Black or Mechanical Zinc Finish, 420 Stainless Steel, and Stainless Steel materials—as per standard ASME B18.8.2 specifications.
- Metric Slotted Spring Pins: Stock sizes include M2 to M8 in Steel with a Thermal Black Finish, as per standard ISO 8752 specifications.
- Mil-Spec MS16562 Slotted Spring Pins: Stock sizes include 1/16 through 1/2 in Steel Zinc Phosphate.
- Inch Hair Pins / Hitch Pin Clips: Stock sizes include .028 to .243 in Steel Zinc.
Our Pins & Clips are competitively priced. Don’t wait! Visit our website today to place an order, or Request a Quote and we will follow up with you.
Can’t find what you’re looking for?
Can’t find what you are looking for on the list? Reach out to us today, and our MF Supply team of sourcing experts will help 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.
Six Reasons To Buy From MF Supply
- Full eCommerce Enabled Website With Technical Manual Available 24/7 – Visit our website and Create a New Account, track online orders, browse our product catalog, check technical specs, subscribe to our blog, or buy online. We are adding items and improving functionality daily!
- Same Day Shipping From The USA – Our hardware products are in stock and ship to you directly from our USA based distribution centers.
- Functional Equivalents To Expensive Brand Names- We stock and source alternatives to brand name fasteners, reducing long lead times and saving you money.
- Creatively Solve Problems – We are sourcing experts, offer competitive pricing and specialize in finding hard to find parts and reducing long deliveries.
- One-Stop Shopping On Certified Hardware – We stock and source a full line of fasteners including Mil-Spec, DFARS compliant and other industrial products.
- WBE/WOSB Woman Owned Certified Small Business – To meet your diversity & set-aside needs.
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.