Which of these fixture parts are NOT used together?

The components of a lighting fixture must be compatible to function correctly together, and the combination of remodeler and bobeche does not align with typical lighting fixture setups. A bobeche is typically used in chandelier or decorative fixtures to hold and protect the bulb while also adding aesthetic appeal. On the other hand, a remodeler is a part used specifically for recessed lighting fixtures, allowing them to be installed in retrofit applications where existing ceilings need to be modified. Since a remodeler and bobeche serve very different purposes and belong to different types of lighting systems, they are not designed to be used in conjunction with each other.

In contrast, the other combinations mentioned all pair compatible components that serve specific functions, enhancing the functionality and safety of the lighting fixture. For example, the rough-in and trim refer to the initial and finishing parts of recessed lighting; the chassis and light shield typically work together in many fixture designs for effective operation; and the track and live end are standard components used in track lighting systems, where the live end helps to make electrical connections. Understanding these combinations is essential for effective lighting design and installation.