Which type of nut is designed with nylon inserts to prevent loosening?

The correct choice is the locknut, which is specifically designed to prevent loosening under vibration or other forces that may cause conventional nuts to come undone. The nylon insert in a locknut creates friction against the threads of the bolt or screw, providing additional resistance against loosening.

In the context of practical applications, this feature makes locknuts ideal for use in machinery and automotive components, where maintaining tight connections is crucial for safety and functionality. The nylon insert effectively captures the bolt's threads, adding a level of security that regular nuts lack.

Other types of nuts do not incorporate this feature. A plain nut, for example, does not have any mechanisms to prevent loosening and relies solely on torque to stay in place. A nylon nut, while it may sound similar, is not a commonly recognized term within engineering; rather, it could refer to nuts made entirely from nylon or those with nylon inserts, but they typically do not provide the same level of reliability as locknuts. Similarly, split nuts are used in specific applications but also do not employ the nylon insert mechanism that is characteristic of locknuts.