A cotter pin is an eye-shaped piece of metal that fits through an eyelet that’s generally made of soft metal, such as copper or brass, to prevent accidental removal of a nut or a bolt. In simpler terms, it’s a fastener for securing a bolt. However, not all bolts are suitable for a cotter pin. So, if you plan to use a cotter pin, go for a bolt with a pre-drilled hole, so the fastener can be inserted.

Aside from securing a bolt, a cotter pin is typically used for small fasteners when there’s insufficient space for a washer. Moreover, you can use it for things like crankshafts where there’s no room for a standard nut and bolt setup because of insufficient clearance to fit both parts side by side, without affecting other parts of the machine.

There are a few types of fasteners that are considered cotter pins, and one of them is split pins. Split pins are inserted through the hole by bending them in half.

In contrast, R-clips, which are also called R-pins, are hairpin cotters that have a straight section that can be pushed through a hole in a shaft. They have curved sections as well that fasten around the outside of the shaft to put the pin in place. You can insert a finger through the ring at the head to bring out the pin out of the hole.

Cotter pins are available at hardware and supply stores, such as the Reid Supply store. But before you go and buy one, check out the guide below so that you’ll know how to select the right type for your needs and how to install and remove it properly.

Choosing A Cotter Pin

When choosing a cotter pin, there are some things to consider. The first thing you have to do is make sure that the cotter pin is the right size for your bolt. If a cotter pin is too small, it will not properly secure your bolt. On the other hand, if a cotter pin is too large, it may not be able to fit into the hole of your nut. This will cause problems when you try and install the nut onto your fastener because it won’t be held securely in place by the head of the cotter pin.

The next thing that you should look out for when shopping for a cotter pin is its head size. If there isn’t enough space between two parts where they meet together, such as between two nuts, then this could prevent it from being able to move freely without getting stuck or damaged since one part would be pressing against another part.

After selecting the cotter pin of your choice, follow the simple steps below to install it and remove an existing one.

Installing A Cotter Pin

Step 1

To install a cotter pin, you’ll need your basic tool set. Use the hammer to drive the pin through the hole. As you do this, use your pliers to hold the end of it in place. You’ll be using them again later on.

Step 2

Once you’ve driven it through far enough that its head is no longer exposed on both sides of the shaft, remove your pliers from one end and grab both ends with your other pair of pliers. Bend over one side of each end about 90 degrees away from where it meets with another piece of metal on either side. If possible, try to get them as close together as possible, so they’re both pointing straight down toward whatever part needs securing at an angle that serves their purpose.

Step 3

Then cut off any excess length between the two bends with some wire cutters or trim along a line drawn horizontally across both ends on one side only. Trimming will ensure that no bits catch anything.

Removing A Cotter Pin

Step 4

The first step is to clamp the bolt in a vise, so it won’t turn. Next, use a crescent wrench or socket to loosen up the nut. Be careful not to use a hammer. You wouldn’t want to damage your work surface or injure yourself. When you’ve got some space between the cotter pin and the bolt head, remove it by hand.

Using the appropriate wrench or socket, loosen the nut on one end of the cotter pin.

Step 5

To remove a cotter pin with pliers, first loosen the nut with a wrench or socket. Don’t remove it; just loosen it so that you can easily pull the pin. Then use your pliers to grab the cotter pin and gently remove it from its sleeve.


In machinery, the small details matter. The same goes for cotter pins. These fasteners are small pieces of metal that help keep a machine together. They’re accessible and easy to install and remove as long as you follow these steps.

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