Which of the following fittings is used to adapt a box to a different size of conduit?

The reducer is the correct choice because it is specifically designed to allow for the seamless transition between two different sizes of conduit. In electrical installations, it is common to have different conduit sizes in order to accommodate varying amounts of wiring or to fit into specific spaces. The reducer effectively connects a larger conduit to a smaller conduit, ensuring that the installation remains secure and compliant with electrical standards.

A conduit strap is used to secure conduit to a surface and does not serve the purpose of adapting box sizes. A condulet is a type of junction box that facilitates connections between conduits but doesn’t specifically adapt sizes. A straight connector, on the other hand, connects two pieces of conduit of the same size and is not suitable for transitioning between different sizes. The reducer is therefore essential in creating a safe and efficient conduit system by allowing for the necessary size adjustments.