Abstract: Disclosed is a fastener assembly to avoid accidental loosening due to vibrations. The fastener assembly includes a circular profiled locking washer and a lock nut. The locking washer is detachably attachable to an arm. The locking washer provides a plurality of leaf-shaped grooves on a first surface, and a central axial aperture for receiving a threaded shaft. The lock nut further provides a plurality of spring loaded balls on a surface facing the first surface of the locking washer. During operation, the lock nut is tightened on the threaded shaft by rotating in clockwise direction, and cessation of rotation, latches the plurality of spring loaded balls with the plurality of leaf-shaped grooves to lock the lock nut, and hence to withstand counter-rotative torque on the lock nut caused by vibrations.