Abstract: A self-clinching fastener is provided, of the type for connection to a section of sheet material having an aperture formed therein for receiving the fastener. The self-clinching fastener comprises a head portion and a shank portion having a smaller outer diameter than the head portion and extending axially from one side of the head portion. A displacement portion extends axially from the one side of the head portion extending radially outwardly of the shank portion. An undercut annular groove is formed inwardly of the displacement portion, extending axially in the direction of the head portion and radially surrounding the shank portion. A generally annular sizing ring is formed about the shank portion axially spaced from the one side of the head portion by an amount somewhat greater than the axial extent of the displacement portion. The outer diameter of the sizing ring is greater than the outer diameter of the shank portion and also greater than the inner diameter of the undercut annular groove.