What is the purpose of cotter pins in mechanical applications?

Cotter pins are specifically designed to secure castellated nuts, pins, and shafts in mechanical applications. A cotter pin works by being inserted through a pre-drilled hole, and then its ends are bent to fasten it in place. This prevents components from loosening or coming apart during operation, making it especially useful in applications where vibration or movement may occur.

In the context of retaining components like castellated nuts, which are designed to be used with a safety mechanism such as a cotter pin, the pin ensures that the assembly remains locked and prevents accidental dislodging. This usage increases reliability in various machinery and structural applications.

The other options represent different functions that are not specific to cotter pins. While bolts can indeed be secured using other fastening methods, they don't rely on cotter pins for that purpose. Similarly, providing electrical contact or acting as a spacer are roles fulfilled by other components, not cotter pins.