Which type of connection is most commonly used with threads or fittings in conduit systems?

Locknuts are commonly used with threads or fittings in conduit systems because they provide a secure and reliable way to join threaded conduit fittings and components. By tightening the locknut against the fitting or conduit, they create a stable connection that helps to prevent loosening over time, which is especially important in vibration-prone environments. This characteristic of locknuts makes them essential for ensuring the integrity and safety of electrical installations.

The other options, while they may serve specific purposes in electrical and construction applications, do not provide the same type of secure connection for threaded fittings as locknuts do. Adapters might be used to connect different types of conduit or to transition between sizes, but they do not specifically secure or lock a connection in the same way that locknuts do. Sealing wax is not a standard practice for making connections in conduit systems, and bolts, while they are used to fasten components in various applications, are not specifically designed for use with threaded conduit connections.