Everything you need to know about castle nuts on trailer axles

Jul 7, 2023 | Uncategorized

This article answers the popular question, what are castle nuts on a trailer axle?

What is a castle nut?

Axle castle nuts are used to keep your trailer wheel hub firmly in place. These nuts are designed to be used with a split pin to ensure it does not become loose while in use. 

What do I use to tighten an axle castle nut?

You can use a channel lock or a wrench to simply tighten the castle nut and insert a cotter pin to keep it in place. 

What is a cotter pin?

A cotter pin, also known as a split pin, is a fastener used for locking the nuts onto the bolt. 

According to Albany County Fasteners, castle nuts are used in conjunction with a cotter pin to prevent loosening. This castle 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.

Why is tightening the axle castle nut important?

If your castle nut is not tightened properly, it can lead to premature wear on the bearings. There is no specific torque rating for the castle nut that holds your hub in place. We recommend tightening the castle nut down until it stops and then backing it off to the next notch wheel where the cotter pin will fit into the castle nut. 

Can I over tighten the castle nut?

Yes – over-tightening the nut can lead to the spindles and bearings overheating, which can damage them.

Watch this video by BlueSwift Axles to learn how to tighten a castle nut on your trailer axle.