This micromechanical part is intended to be fastened to a spindle and has at least one opening (10, 20, 30) whose edges comprise an alternating arrangement of rigid areas (11) and elastic areas (12, 22, 32). It is possible for those ends (13) of the rigid areas (11) closest to the center C of the opening (10, 20, 30) to be connected by a first circle C1 having a diameter greater than the diameter of a second circle C2 connecting those ends (15, 25, 27) of the elastic areas (12, 22, 32) closest to the center of the opening. In this micromechanical part, each rigid area (11) is formed by a convex portion projecting into the opening (10, 20, 30).