Abstract: Apparatus attaches together stacked upper and lower metal sheets and provides a reinforced aperture. A lower die has a die groove and an opening in the center of the die groove. An upper die has an annular end face that registers with the die groove and a spring-loaded reciprocable punch button that registers with the opening. A hollow ring-shaped grommet has an annular upper end flange engaged by the annular end face of the upper die and an axially extending tubular wall longer than the stacked thickness of the sheets. A metal piercing point at the terminal end of the axially extending wall pierces through the stacked upper and lower sheets and into engagement with the die groove of the lower die to progressively bend the axially extending wall radially outward and upward into engagement with the lower sheet, thereby attaching the sheet together and providing a reinforced aperture.