Why are split pins used in conjunction with castellated nuts?

Split pins are used in conjunction with castellated nuts primarily to prevent loosening. Castellated nuts have notches on their outer circumference, which align with a hole in the bolt or shaft. When a split pin is inserted through this hole and then secured, it effectively locks the nut in place. This locking mechanism is crucial in applications where vibrations or dynamic loads are present, as these conditions can cause fasteners to loosen over time.

The use of split pins fosters safety and reliability in mechanical assemblies, ensuring that components remain tightly secured during operation. This practice is widespread in various industries, including automotive and machinery, where the integrity of threaded connections is essential for functionality and to prevent potential failures.

The other options, while relevant in certain contexts, do not apply directly to the primary purpose of split pins with castellated nuts. Split pins do not inherently increase strength, improve sealing, or reduce friction; their main function is to maintain the position of the nut and prevent loosening due to movement.