Castle Nuts

Locking Nuts for use with a Cotter Pin or Safety Wire

Castle nuts are used in conjunction with a cotter pin to prevent loosening. This nut has slots (notches) cut into one end. The name comes from the nut's resemblance to the parapets of a castle.

Castle nuts are installed much like any other hex nut, being fastened to a bolt or axle. The installation differs in that the bolt or axle has one or two holes drilled through its threaded end. If the castle nut's slot isn't aligned with the bolt or axle's hole, the nut is rotated to the nearest slot. The nut is then secured with a cotter pin or safety wire to the bolt or axle. This cotter pin is then bent to secure the castle nut to the bolt. This completes the locking action.

Castellated nuts are used in low-torque applications, such as holding a wheel bearing in place.

---

Castle Nut Installation

Castle Nut & Cotter Pin Installation Transcript Scroll Down To Continue Reading Bob: Here we have a castle nut. These are typically used in cars. You find them on axles when they hold on wheels and bearings; rotors. We're going to demonstrate this one also for you. We're going to drill out a bolt and slide the cotter pin in to show you how this is locked in place. Here I have a castle nut in which we're going to drill a hole for this cotter pin go through the cut-the castle nut. I am going to--in where these little grooves are in the castle nut I'm going to set myself a little starter. I'm going to take my drill... So this is 1/8; this cotter pin is one-eighth of an inch in diameter. I'm going to drill a three-sixteenth hole. What's key here is that you hold the drill level. So when you come out the other side that you come out right where the exit is through that prong. Of course, I need to add some lubricant. Make sure my bit lasts me for a while. I'm drilling stainless steel here. I'm eyeing straight across, as I'm drilling this, I'm eyeing straight across the screw to make sure I'm running in the right direction. In most cases, most cases this hole is there for you already and you don't have to drill it but in some situations you may have to do that. So I'm sliding that through, there's your cotter pin. Gonna grab my little pliers here. I'm going to bend this around. To lock this in place. To make sure that your wheels don't pop off if it's going on your car. This is your protection of that. Now that's not going anywhere. Locked in place. And that's the whole mechanism behind a castle nut.

---

FAQs

What is a castle nut used for?

Castle nuts, or castellated nuts, are used in low-torque applications as a kind of lock nut. They, combined with a cotter pin, lock an assembly down. A notable example of their use is in holding a wheel bearing.

What is the difference between a slotted nut and a castle nut?

The main difference between the two is that castle nuts have a round section at the top where the slots are. Slotted nuts have their slots cut into the nut itself. While functionally the same, the added rounded top of the castle nut allow the installed cotter pin to be installed closer to the nut, almost flush, for added secureness.

What fasteners are used to lock castle nuts?

Tradiationally, castle nuts are locked with cotter pins or split pins. R-Clips and safety wire have also been known to be used for installing castle nuts.

What are locking nuts for?

Lock nuts are an easy to use, cost-effective solution to protecting against vibration-related loosening. They're used to protect applications from loosening over time.

How do you use lock nuts?

Most lock nuts are used the same way traditional nuts are; by simply fastening them to the opposite side of a bolt. The locking action activates after the nut is fastened down. The exception to this is castellated nuts and slotted nuts, which needs a hole drilled into the bolt and a cotter pin to finish installation.