Cotter Pins vs. Split Pins: Is There a Difference?
Cotter pins and split pins are among the most commonly used reusable metal fasteners for securing bolts, axles, and other machine components and elements together. However, while they might look interchangeable to those less proficient in mechanical engineering, there are some key differences between these two types of pins. In this guide, we’ll dive deep into the difference between cotter pins and split pins.
What Are Cotter Pins?
Cotter pins, often called cotter keys, are locking pins frequently used to secure other fasteners in place. They come in various sizes, and thanks to their design, cotter pins are a fantastic option for securing screws and slotted bolts.
Cotter pins are mostly used as low-cost locking mechanisms in several applications. Their most basic design is made of soft metal wire (usually mild steel) bent back on themselves near the middle of the wire.
A loop, or an eye, is from at one end of the pin, with two pointed ends of the half-circular cross-section wire coming together at the other end. It’s important to note that one prong is purposefully slightly longer than the other to make it easier to grab with pliers or fingers.
What Are Split Pins?
Split pins, often called split cotter pins, hairpin cotters, or R-clips, are actually a sub-type of cotter pin. Unlike basic cotter pins, which are used to secure components with a through-hole, such as nuts and bolts, split pins are mostly used to secure castle nuts and clevis pins.
The two types of pins are also designed differently. Basic split pins have straight tines but split pins have one straight tine and another that’s bent into a circular shape. During application, the straight end is inserted into a through hole, while the bent part of the R-pin goes around the fastened element, securing the pin in place.
Cotter Pin Applications and Materials
Both cotter pins and clevis pins can be made of different types of steel, and the specifications of each used material differ depending on the application and manufacturer. However, some general rules apply. For example, cotter pins are typically inserted through a through-hole, and their tines are bent back, thus securing them in place. This means they must be made of softer, more pliable steel alloys.
Split pins, on the other hand, are used differently. The straight prong is inserted through a through-hole, while the looped end of the R-pin grips one side of the shaft, bolt, or clevis pin, thus resisting removal. Since they’re not bent during their application, split pins are typically made of higher-carbon or stainless steel and more durable materials in general; they are much “springier.”
Lastly, due to the difference in design and materials, the removal of these pins also differs. With cotter pins, you’d typically use pliers to straighten both the shorter and extended prongs to allow for the removal of the pin.
Since split pins (R-clips) aren’t bent during their application, they’re also much more easily removed. The looped end of the R-pin actually provides quite a convenient way to remove the pin. Pull the looped end with your finder or pliers, depending on the pin size.
The Difference Between Cotter and Split Pins
While they might look similar, there are some important differences between cotter and split pins. Cotter pins are secured by their pins being bent back, while split pins are inserted by applying enough pressure to snap the R clip around the bolt or pin. There are also significant differences in applications and use cases, as well as the materials they’re made of.
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