Structure

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A structure is a term used to define the body of a Transformer. Without a Personality component, the structure is a lifeless shell. The superstructure is the outer portion of the structure, generally containing components for the transformer's alternate mode, and is often changed during reformatting in accordance with disguise protocols. The substructure contains a transformer's inner workings, and usually includes any special equipment or weapon systems.

At times, the spark-less bodies of deactivated Maximals have been referred to as shells.

A Transformer's structure varied depending on which form their personality inhabited. The Renegade Decepticons when freed by Starscream developed new structures when their personality components were placed in Earth vehicles.

Fiction

Generation 1 cartoon continuity

After being captured, the Renegade Decepticons had their personality components removed from their structures which were destroyed. Starscream's Brigade

Beast Machines cartoon

While exploring Cybertron in the wake of Megatron's conquest, Primal's team of Maximals came across an entire facility stacked with deactivated Maximal bodies, which (playing on both "graveyard" or "junk yard") they later referred to as the "shell yard". Spark of Darkness

From Teletraan I: The Transformers Wiki, a Wikia wiki.