Use the Center of Mass: Boundary subnode to select a set of boundaries whose centroid represents the center of mass of a Mass and Moment of Inertia (Rigid Material).

The Center of Mass: Edge subnode to select a set of edges whose centroid represents the center of mass of a Mass and Moment of Inertia (Rigid Material).

The Center of Mass: Point subnode to select a set of points whose centroid represents the center of mass of a Mass and Moment of Inertia (Rigid Material).

These nodes are automatically added when Centroid of selected entities is selected in the parent Mass and Moment of Inertia (Rigid Material) node. They cannot be added or removed manually.