Which component is NOT part of a unibody structure?

In a unibody structure, the design integrates the body and frame into a single cohesive unit, which contributes to the overall rigidity and strength of the vehicle. The components listed, such as the radiator support, strut towers, and unirails, are all integral parts of a unibody construction.

The frame, however, refers to the separate structural support system typically found in vehicles with a body-on-frame design. In this type of construction, the frame is a distinct entity that supports the body, whereas a unibody structure relies on the strength and rigidity of the combined body and structural elements without a separate frame component. Therefore, identifying the frame as not part of a unibody structure is accurate and highlights the differences between these two automobile construction methods.