A splayable fastening device comprises a fastener engagable element having a screw-threaded element, at least one flexibly springable arm member which is at least in part wrapable about a screw-threaded axis of the screw-threaded element, and a retainer for retaining the said flexibly springable arm member in its wrapped or coiled condition. The retainer is movable relative to the flexibly springable arm member whereby the flexibly springable arm member is unfurlable in a clockwise or anticlockwise direction. A method of fastening to a hollow wall using such a splayable fastening device is also provided.