Castellated Nuts Explained: Design, Function, and Selection Tips

Nuts are a common fastener that work in tandem with bolts. By attaching to a bolt, a nut prevents the fastener from loosening or backing out. Among the various nut types, the castellated nut stands out for its unique design and added security.

Overview of Castellated Nuts

A castellated nut—sometimes called a castle nut—features a series of raised notches around its outer edge that resemble the battlements of a medieval castle. These notches create a keyhole that accepts a retaining pin, locking the nut in place and providing an extra layer of anti‑rotation protection.

How Castellated Nuts Work

After the nut is tightened onto the bolt, a pin is driven through a central hole that runs through both the nut and a specially designed threaded bolt. The bolt contains a radial hole that allows the pin to pass through. The pin then locks the nut, preventing it from turning or sliding back along the bolt.

Because the pin must pass through a hole, only bolts with a central clearance are compatible. Standard solid bolts will not work; instead, you need a bolt that has a drilled hole or a threaded core that allows the pin to be inserted.

Tips on Choosing Castellated Nuts

When selecting a castellated nut, consider the material first. Carbon‑steel versions offer high strength and durability, while stainless‑steel variants provide superior corrosion resistance. Pick the material that matches the operating environment.

Size matters. A castellated nut must match the bolt’s thread size and pitch; otherwise, it cannot be properly secured. Always double‑check the bolt size before purchasing.