Abstract: A device for safeguarding screw connections and other rotatable and/or longitudinally movable parts against accidental loosening. The device includes a conical dish or plate spring which by means of the free end face of its inner and/or outer marginal zone rests against a counterthread on the carrier of the part to be safeguarded. The dish spring has a plurality of radially extending tongues, the ends of which, while not forming a thread, are merely so rounded that said tongues during the screwing-in operation will adapt themselves elastically to the thread of the carrier of the part to be safeguarded, and during the flattening of the spring will interwedge in the thread while causing no permanent deformations of the carrier thread.