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 crenellated parapet of a medieval castle. The bolt or axle has one or two holes drilled through its threaded end. The nut is torqued properly and then, if the slot isn't aligned with the hole in the fastener, the nut is rotated to the nearest slot. The nut is then secured with a cotter pin or safety wire. Castellated nuts are used in low-torque applications, such as holding a wheel bearing in place.
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Trade Names: Castellated nut or slotted nut
Castle Nut Installation
Castle Nut & Cotter Pin Installation Transcript
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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.