The Bodygroup of the Scout TF2

A bodygroup is a feature of the Source Engine that enables specific sections of a model to be enabled or disabled, allowing for different models to take their place. In Team Fortress 2, bodygroups are used in the models of several items to show or hide specific player or weapon models when needed; for example, most hats manipulate bodygroups to remove the default headgear present on the player model to allow room for the newer hat model.

Bodygroups do not alter hitboxes; they are merely a cosmetic feature.