Importance

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Abstract

An improved fastener includes a polygonal rim which cooperates with an axially projecting center section to define a recess in which sheet material is forced by a die to hold the fastener against rotational and axial movement relative to the sheet material. To improve the gripping action between the fastener and the sheet material, the sheet material is stretched by a tool which extends through the center of the fastener. When a hole is cut in the sheet material by the fastener, the prestretched metal resiliently contracts to grip the center section of the fastener. The gripping action between the sheet material and the fastener is further improved by resiliently compressing the center section of the fastener with the die. As the center section is withdrawn from the die, the center section springs outwardly to decrease the size of the recess and grip the sheet material. In addition, the rim is resiliently deflected radially outwardly by the die as metal is forced into the recess. When the die is withdrawn from the recess, the rim springs inwardly to decrease the size of the recess and grip the sheet material. The holding action between the fastener and the sheet material is increased by providing the recess with indentations which project into the rim and center section. The holding action is also increased by having the center section flare axially and radially outwardly.

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First Claim