Abstract: An improved fastener system is derived for cold working the surfaces defining aligned fastener holes in structural members and installing fasteners therein. Essentially, an integral fastener and mandrel construction facilitates the insertion of a sleeve into the holes, an expansion of the sleeve thus disposed to thereby cold work the surfaces of the members defining the holes, and the pulling of the fastener into the holes thus prepared and sleeve-lined. A frangible neck is provided between the fastener element and the mandrel element which permits the breaking off and discarding of the latter after the former is installed. Retenion means is then installed, formed or otherwise provided on the fastener end in conventional manner. Thus, cold working and fastener installation is accomplished in only two steps due to the critical design and configuration of the combined fastener, break-off groove and mandrel.