What type of fittings are used to connect hose couplings that have unlike threads?

Adapters are utilized to connect hose couplings that have unlike threads. They serve as a bridging component that allows hoses with different thread types or sizes to be connected effectively. In firefighting operations, where different equipment may be used together, adapters are crucial for creating a functional system, ensuring that firefighters can utilize various hoses and tools regardless of the threading differences.

Reducers, on the other hand, are designed to reduce the diameter of the hose or fitting but do not address the issue of differing thread types. Elbows are primarily used to change the direction of the flow in a plumbing system; they do not serve any purpose in threading compatibility. Caps are used to seal the end of a hose or fitting, providing closure rather than facilitating connection between two different thread types. Hence, the correct choice reflects the unique function of adapters in overcoming the compatibility challenges in various firefighting situations.