Abstract: A filter comprises a receptacle including a positive terminal pin, a negative terminal pin and a ground terminal pin; a filter box installed at one side of the receptacle; the filter box being installed with electric elements; a filter cover serving to seal theses electric elements within the filter box; a ground terminal pin being installed at another side of the filter box; the electric elements and grounding terminal being connected to the positive terminal pin, negative terminal pin and ground terminal pin so as to form a filtering circuit; a positive electrode of the filtering circuit being welded with a positive conductive wire and a negative conductive wire; a metal casing having a receiving groove for being engaged to the filter box and the receptacle; and an isolating cover being engaged to the metal casing; thereby the teeth piercing into a periphery of the isolating cover.