How to Install Cotter Pin – 4 Quick & Simple Steps to Follow

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You can use cotter pins to secure a bolt and nut assembly. Some common uses are as part of the locking mechanism found in castle nuts of automotive hubs, and to fix the crankshaft of a bike.

Cotter pins, also known as split pins, are made of bendable metal, such as aluminum and malleable steel. This makes it simple to bend the split ends with pliers to the secured final position.

You can use split pins for DIY crafts to make puppets with moving parts, statement necklaces, knitting looms, and garden pinwheels. It can be used to replace hairpins in DIY crafts when you need something larger, sturdier, and weather-resistant.

Cotter pins are also used when you want to secure a trailer hitch. These are hairpin cotter pins that are constructed for heavy-duty use and zinc plated for corrosion resistance and secure, stable hold.

Read on to find out how to install a cotter pin properly.

For use to secure bolts, you will slide the cotter pin through the hole of a slotted nut. Pull it through to the end of the loop. Then use pliers to grab the split end. Bend it to a locked position around the castle nuts.

You should use a cotter pin only once. Because reusing a single cotter pin may weaken the metal can cause it to break off.

The next section will talk about the installation guide to help you install the cotter pin properly.

How to Install Cotter Pin in 4 Simple Steps

Step 1: Choose the right size cotter pin

Selecting the correct size cotter pins is important. You can get a cotter pin kit with an assortment of sizes.

Select the size of the cotter pin by placing it on top of the castellated nut. If it fits in the grooves without being too large or small, you know that you’ve got the right size.

Step 2: Optional, Drill a hole in the bolt

In most situations, the hole will already be there in a bolt for a slotted nut. And it will be ready for installing the cotter pin.

But there are times where you will need to drill the hole to secure the connection of the bolt and nut.

Choose a drill head that is a bit bigger than your cotter pin. For example, a 1/8th cotter pin uses a drill head that is 3/16th hole.

The hole will be near the end of the bolt while leaving a section of threads at the end.

Hold the drill level because you want the drill to go straight across.

Add some lubricant to help drill metal against metal.

Step 3: Insert the cotter pin in the bolt hole

Insert the split end of the cotter pin into the hole in the bolt. It should feel like a good fit, not too snug or too loose.

Pull it through until it touches the looped end of the cotter pin.

Step 4: Bend the split ends of the cotter pin

The final step to securing the cotter pin around the castellated nut.

Use pliers to grab a split end and bend it around the castle nut. Do this for the other end, as well.

Then use the pliers to squeeze and split ends until they are secure around the nut and bolt connection.

It’s important to bend the legs in a single, simple motion. Because fiddling with them may weaken the metal and cause them to break off. Replace used cotter pins with new ones because they are meant for single-use only.

Once you have installed the cotter pin, it will prevent the castellated nut from coming loose from the bolt.

Following this process, you can install a cotter pin properly and in the right place.

Because safety comes first, the usage of a cotter pin should be known to the person who is going to work with one.

Cotter pin vs. hairpin: Top view of proper installation of cotter pin and hairpin cotter pin as a hitch pin

How to Install Hairpin Cotter Pin?

Hairpin cotter pins are used as hitch pin lock systems, such as the trailer hitch. Hairpin cotter pins are designed to give a good and strong grip to the hitch. Hairpin cotter pins look like an R shape, so it’s also called the R-pin.

When you install the hairpin cotter pin properly, it will attach the trailer so that it does not dislodge from your vehicle.

Line up the pin hole to the hitch. Install the pin with the bendy end facing down.

Then get the hole on the hitch pin to be straight up and down.

The hairpin cotter pin, also known as a hairpin clip, has to be inspected first. Inspect the hairpin clip to make sure the bottom bend of the clip is touching the straight end. This means the hairpin clip will attach securely.

Holding the hairpin cotter pin, you can insert the straight end into the hole on the pin. You may have to turn the hitch pin to slide it in. You should have a bit of a hard time sliding it in because of the secure springy design of the hairpin clip.

Check out the (C.) image above or video below for the proper way to install a hairpin cotter pin and inspect a trailer hitch.

Finally, inspect the installation. Inspect that the last bend touches the straight end. If there is a gap, it means you will have to use a larger size hairpin clip.

If you are not sure what size hairpin cotter pins to use, having an assorted set of hairpin clips would help.

How to Use Cotter Pin?

Cotter pins help to secure the nuts from sliding off bolts, particularly in heavy machinery like cars and trailers.

The cotter pins are inserted near the end section of the bolt to hold up castellated nuts, and other types of hitch pin installations.

This way, the split pin creates a lock near the end of the bolt, which prevents the nuts and bolts from falling off due to the vibration of the automobile. This causes accidents when parts falling off of machines.

You may have to drill a hole in the bolt if it does not already have a hole. Choose a drill bit that is slightly larger than the size of the cotter pin.

Apply lubricant to improve the surface finish of this metal on metal drilling.

The bulbous end of the cotter pins secures one side of the hole in the bolt.

Use pliers to bend the split end of the cotter pin. Bend each end around the castle nut.

This creates a lock for the bolt and nut used to stay together securely on the machine.

Another type of cotter pin is hairpin cotter pins that are used as part of a trailer hitch. These are hairpin clips that slide into the trailer hitch pin to create a secure, stable hold.

Split pins can also be used in DIY crafts to make the moving parts of puppets. Split pins are also used to craft pinwheels for your yard, looped to make statement necklaces, and combined with cans to create knitting looms.

So, for a hairpin cotter pin, you can only insert it by only one side as it has only one plain pin of the two. All you have to do is to insert the pin into the bolt hole and bent the pins according to the need in the opposite directions. And then use pliers to bend the extra length of the pin.

How to Install Cotter Pin

What is the Cotter Pin Bending Tool for Proper Installation?

You can use pliers as the cotter pin bending tool.

Once the cotter pin is inside the bolt hole, use pliers to separate the split ends of the cotter pin.

Then use the pliers to easily wrap the split ends around the castellated nut. Finally, ensure the ends sit flush to complete the cotter pin installation.

Having a set of pliers means you can choose the best size pliers to do the job.

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