What's the purpose of a using a castellated nut versus a regular nut?

I was watching Classic Car Restoration on the DIY Network. The guy is installing new spindles on the front of this car and is using castellated nuts to hold the spindle in place.

Why use this type of nut instead of a regular one?

A castellated nut allows for a cotter pin to hold the nut in place (to keep it from loosening, that is).

The spindle has a hole through it and the slots in the nut are lined up with it for insertion of a cotter pin as a keeper. It keeps the nut from coming loose because of vibration or shock.

Crap, sorry, I hit submit too soon.

The part that the nut fits onto (in this case, the spindle) must have a hole drilled in it for a castellated nut to work. The castellated nut is tightened, but left with one of the depressions in the castellation aligned with the hole. A cotter pin is placed through the hole. The ‘eye’ end of the pin cannot go through the hole. The legs of the pin are spread, with one going in each direction around the nut. Sometimes the longer leg of the pin is bent into one of the castellations, but this is decorative, and purely optional.

Couldn’t a regular nut have a hole in it for the same purpose, or does the castellation give it more strength?

The nut would need a slot because you never know for sure where along the thread it will be tight enough. And you need a lot of slots because you never know how far it will be turned around the circumferance when tight enough. You tighten the nut to the specified lower torque and then line the next tighter slot up with the spindle hole.

The nut doesn’t have the hole in it, the nut has the slot. The bolt, shaft or spindle has the hole in it. There are nuts with holes in them, these are meant to be secured with wire – called safety wire. These also require holes in the bolt, shaft, or spindle, or at least someplace to anchor the wire.

I found this and it has a hole in it. Wouldn’t that be where you insert the cotter pin?

The guy on the show suggested that you bend one end of the pins over and cut the other one off.

The linked picture shows castellated nuts. They don’t have holes (ignoring the threaded “hole” of the nut that screws onto the bolt or shaft). They have slots. The cotter pin goes through a slot, through the hole ( = round hole as would be produced by a drill) in the shaft or bolt, and on through a corresponding slot on the nut, 180 degrees opposite the first slot.

Cutting off one leg of the pin is sometimes done for cosmetic reasons, or in certain applications because there’s not room to bend that particular leg without possibly interfering with something. In most cases, there’s no compelling reason to cut it rather than bend it or even leave it sticking out straight.

Old “mossy-horns” like me will akso tell you that the castellated nut,when put on upside down ,will also serve to clean up any slightly damaged threads on the bolt or stud.

It can then be removed nd installed properly.

It also allows for a finer adjustment in the tightening range.

Ol’ EZ