A computer-implemented method for designing, with a CAD system, a 3D modeled object representing a mechanical part. The method includes displaying a B-rep having faces and edges and representing at least a part of the mechanical part, selecting, by graphical user interaction, at least one face of the B-rep, and, automatically by the CAD system, recognizing a set of faces including the at least one face and representing a bump. The recognizing includes determining a first set of faces representing a depression and a second set of faces representing a protrusion, and selecting, among the first set of faces and the second set of faces, a set of faces having a shortest boundary curve perimeter and being different from both the selected at least one face and the B-rep. The first set of faces and the second set of faces both comprise the at least one face.