A two-part mechanical fastener comprising an elongated body with a bore slidably carrying a mandrel adapted to interferingly engage the body is described. The fastener body has one or more protuberances on its exterior surface. In an aspect, the protuberances form a thread. The fastener is adapted to form an opening in, and penetrate, a stack of two or more workpieces. To secure the workpieces in the workpiece stack and form a robust joint, the fastener body is deformed by the mandrel, expanding the body, so that a body end engages a surface of the workpiece stack and the one or more protuberances are brought into engagement with the walls of the opening. Methods of using such a fastener to secure non-ferrous or polymer-based sheet-like workpieces to one another are disclosed.