Clinch type fastener

Claim 1

In a clinch type fastener for attaching insulating material to thin sheet metal in which the fastener includes a generally cylindrical shank having a driving portion at one end and a penetrating portion at the opposite end, said penetrating portion having a generally frusto-conical exterior wall tapering inwardly toward the axis of said shank and terminating in a relatively blunt end, said penetrating portion having a cavity extending axially inwardly from said blunt end and defining a cavity wall, said penetrating portion having a pair of diametrically opposed slots extending inwardly from said blunt end generally parallel with the axis of said shank, said slots extending from said frusto-conical exterior wall to the cavity wall, the improvement comprising an enlargement located at the base of each slot, each enlargement having at least one portion extending outwardly of said frusto-conical exterior wall and defining stop means to limit penetration of said fastener into said sheet metal, said enlargements being spaced from said blunt end a distance substantially less than the thickness of the sheet metal, the side walls of the cavity adjacent to said slots tapering downwardly and inwardly toward the axis of said shank at an angle of substantially 5°, the side walls of the cavity remote from said slots tapering downwardly and outwardly from the axis of said shank at an angle of substantially 6°, said inwardly and outwardly tapered walls defining a pair of opposed U-shaped members at said blunt end and defining a generally elliptical configuration, and a shallow groove extending inwardly from the blunt end in a location remote from said slots, whereby a driving force applied axially of said shank causes the blunt end of said penetrating portion to penetrate partially through the sheet metal, extrude a pair of bulbous masses into said cavity and cause the inwardly inclined walls of said cavity adjacent to said slots to collapse inwardly about the bulbous masses and firmly attach the fastener to the sheet metal without penetrating entirely therethrough.