289-679, RS PRO, Copper Crinkle Locking & Anti-Vibration Washer, M4, BS 4463, Brand RS Pro, For Screw/Bolt Size M4, Washer Type Crinkle, Inside Diameter 4.36mm, Outside Diameter 7.99mm Copper Crinkle Locking & Anti-Vibration Washer, M4, BS 4463