Abstract: A vibration resistant fastening device includes a fastener (1) comprising a shank (20) and a drivable head (21), the shank (20) having a first handed thread closer to the head (21) and an opposite handed thread further from the head (21). A nut (2) is threadably engaged upon the first handed thread and annular washers (3 and 4) carrying first and second interengageable cam-faces are disposed around the shank (20). In use the opposite handed threaded portion of the shank (20) is threadably engaged in a receiving member (25) and the washer cam-faces (5) are clamped together between the nut (2) and the receiving member (25). The first annular washer (3) is fixed to the nut (2) and the second annular washer (4) is fixed to the receiving member 25, via an intermediate member (26), and the cam-faces (5) co-operate to increase the tensile stress in the shank (20) when the nut (2) is turned in the loosening direction under the influence of vibration.