Staked fastener with undercut

A blank for forming a self-clinching fastener of the type for connection to a section of sheet material having an aperture formed therein for receiving said fastener, said blank comprising:

• a head portion of a preselected outer diameter;
• a shank portion of outer diameter smaller than the outer diameter of said head portion and extending axially from one side of said head portion, said shank portion having an enlarged diameter portion extending a predetermined distance axially outwardly from said one side of said head portion;
• a displacement portion extending axially from said one side of said head extending radially outwardly of said enlarged diameter shank portion;
• and an undercut annular groove formed inwardly of said displacement portion, extending axially in the direction of said head portion and radially surrounding said enlarged diameter shank portion;
• wherein said groove is defined by a first tapered surface converging in the direction of said head portion and a second, tapered surface, spaced from said first tapered surface and also converging toward said head portion.

The combination of a section of sheet material having an aperture with a self-clinching fastener engaged with said section of sheet material and extending through said aperture, wherein said self-clinching fastener comprises:

• a head portion;
• a shank portion having a smaller outer diameter than said head portion and extending axially from one side of said head portion;
• a displacement portion extending axially from said one side of said head portion and extending radially outwardly of said shank portion;
• an undercut annular groove formed radially inwardly of said displacement portion, said groove extending axially in the direction of said head portion and radially surrounding said shank portion, wherein said groove is defined by a first tapered surface converging in the direction of said head portion and a Second, tapered surface, spaced from said first tapered surface and also converging toward said head portion;
• and an enlarged diameter, generally annular sizing ring formed about said shank portion, axially spaced from said one side of said head portion by an amount somewhat greater than the axial extent of said, displacement portion said sizing ring having an outer diameter greater than the outer diameter of said shank portion and also greater than an inner diameter of said undercut annular groove.

A self-clinching fastener of the type for connection to a section of sheet material having an aperture formed therein for receiving said fastener, said fastener comprising:

• a head portion of a preselected outer diameter;
• a shank portion of outer diameter smaller than the outer diameter of said head portion and extending axially from one side of said head portion, said shank portion having an enlarged diameter portion extending a predetermined distance axially outwardly from said one side of said head portion;
• a displacement portion extending axially from said one side of said head extending radially outwardly of said enlarged diameter shank portion;
• and an undercut annular groove formed inwardly of said displacement portion, extending axially in the direction of said head portion and radially surrounding said enlarged diameter shank portion, wherein said groove is defined by a first tapered surface converging in the direction of said head portion and a second, tapered surface, spaced from said first tapered surface and also converging toward said head portion.