An apparatus for joining a plurality of metal sheets by first drawing and then laterally extruding the metal into an enlarged shape which will permanently and mechanically interlock the two metal sheets. The apparatus utilizes a novel die body construction in which the die body has a cavity wall provided with a plurality of longitudinally extending flutes which communicate with a depressed groove surrounding a centrally raised portion of an anvil. Upon compression and drawing, the material from the metal sheets will extrude from the raised central portion of the anvil into the depressed groove and the extrude laterally into the substantially longitudinally extending flutes which allow the finished assembly to be withdrawn from the die body along the path of the substantially longitudinally extending flutes. A method of forming a joint between metal sheets is also disclosed. Also disclosed is a die body which permits withdrawal of the finished product without requiring movable releasable portions in the die. To improve the bottom of a cavity punched out by a punch, the punch may be provided with an intaglio figure to emboss a corresponding figure in the bottom of the metal sheet.