| 摘要 |
Members of an assembly, a first of which has an aperture and a second of which is of deformable sheet-like material, are fastened together by piercing and deforming the second member using a punch and die to provide a pierced aperture having a peripheral wall of helical form analogous to a screw-thread, assembling the members together with the apertures aligned, inserting a tubular fastener having a head and a shank into the apertures so that the head abuts a face of the first member and the shank extends through the second member, and then expanding at least part of the shank within the pierced aperture of the second member and thereby causing the peripheral wall of the pierced aperture to impress a helical peripheral groove into the external surface of the shank of the fastener. The shank can be expanded by pulling a tapering mandrel head into or through it. The fastener is made to facilitate its removal by unscrewing from the fastened assembly by providing or forming wrenching surfaces in its bore or on its head for engagement with a key, screwdriver, spanner or the like.
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