What is a part of a wiring system that is intended primarily to perform a mechanical function?

The correct choice is a fitting, as it primarily serves a mechanical function in a wiring system. Fittings are components used to join pieces of electrical conduit, cables, or equipment to ensure that electrical systems are properly assembled and secured. They facilitate the physical connection and structural integrity of the wiring, allowing for safe and efficient electrical installations while supporting other components in the system to function correctly.

In contrast, devices, receptacles, and switches are designed primarily for electrical functions. Devices typically refer to electrical appliances or apparatus that consume power, receptacles are points where electrical devices plug into the circuit, and switches are used to control the flow of electricity. While these components may also contribute to the overall structural setup by providing a means to connect and control electricity, their primary intent is to facilitate electrical operations rather than perform mechanical functions. Therefore, the fitting stands out as the component primarily aimed at fulfilling a mechanical role.