What Is a Cotter Pin?

It’s not uncommon for bolts to loosen over time. If a bolt is attached to a machine, for instance, the vibrations produced by the machine may cause it to come out. There are ways to secure bolts in place, however, including the use of a clutter pin. But what exactly is a cotter pin?

The Basics of Cotter Pins

Also known as a split pin, a cotter pin is a simple fastener that’s used to secure a bolt — or any other rod-shaped fastener — in place. As shown in the adjacent image, cotter pins consist of a narrow U-shaped piece of metal with a flared and circular top. Cotter pins are inserted into a bolt to prevent the bolt from loosening.

How Cotter Pins Work

Cotter pins work by preventing the bolt in which they are inserted from coming out. Of course, not all bolts support the use of a cotter pin. Rather, you can only insert a cotter pin into a bolt if the bolt has a hole in it. Without a hole, there’s nowhere to insert a cotter pin. Therefore, you’ll need to choose a bolt with a pre-drilled hole if you’re planning to secure it using a cotter pin. You can always try to drill a new hole into an existing bolt, but there are bolts available that are designed specifically for use with a cotter pin. They already have a pre-drilled hole, allowing for faster and easier installation of a cotter pin.

To use a cotter pin, simply place it through the bolt’s hole. Next, you’ll need to twist the two prong-like ends of the cotter pin outwards and away from each other. Some people assume that it’s best to twist the ends of cotter pins together, but this simple fastener offers the greatest protection against loosening when the ends are twisted away from each other. Using this technique, the cotter pin is less likely to wiggle its way out of the bolt — something that could otherwise cause the bolt to come out as well.

In Conclusion

A cotter pin is a simple fastener that’s used to secure a bolt in place. Consisting of a U-shaped piece of metal, it’s inserted through the hole of a bolt, after which the ends are twisted together. The cotter pin secures the bolt in place so that it’s less likely to loosen and come out.

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