Modify NormalsKeyCreator \ Tools \ Maintenance \ Modify-Normals
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The Modify Normals function is used to reverse the normal sense of direction of all faces in a body. Solids are usually created with all normals pointing out away from the center of the solid. You can reverse the normal direction for a single body or for multiple bodies all at once. When you select several bodies you can select one of three methods for reversing only some of the bodies.