Abstract: A bolt fastener of known kind for engagement in a socket is screwthreaded at its outer end, which protrudes for engagement with a nut. The fastener has a waisted portion, including a taper, towards the inner end of the fastener, the taper converging away from the inner end. The waisted portion is loosely surrounded by a collar with a slit along it. The collar grips the socket when the nut is tightened to withdraw the fastener relatively to the collar, the collar thereby being expanded by the taper. The present fastener is used wholly within the socket and, instead of being screwthreaded externally, has a bore which extends axially from the outer end and is screwthreaded for engagement with a headed bolt.