Grommet type fastener

Claim 1

A one piece plastic anchor member for application to an apertured workpiece in position to accommodate a threaded shank of a screw member, said anchor member including a head section providing a surface for clampingly engaging one side of a workpiece, and a shank section extending axially from said head section, said shank section including an elongate hollow portion defined by an expandible wall for accommodating a screw shank and diametrically disposed normally outwardly flaring shank arms integrally connected with the entering extremity of said hollow portion and having free work engaging extremities positioned in the vicinity of the underside of the head section, said head section being provided with a polygonal axial extension acceptable within said workpiece aperture, said extension having an axially facing tapered end surface which extends inwardly and downwardly towards the entering end of said shank in opposition to the extremities of said arms, the extremities of said arms being adapted to contact and ride down said tapered end surface when said shank arms are collapsed upon insertion within a complementary work aperture, the maximum length of said shank arms being greater than the dimension from the radially innermost portion of said tapered end surface to the connection of said shank arms with said hollow portion while said length is substantially equal to the dimension from the radially outermost portion of said tapered end surface to said connection, whereby said shank arms are foreshortened and bowed as they ride down said tapered surfaces during insertion and spring outwardly after their extremities pass through said aperture, so as to underlie said panel, and the wall defining said hollow portion being laterally expandible in the form of a bulge in the vicinity of the clamping surface of the head section and abutting the inner opposed surfaces of said arms as an incident to the application thereto of a screw shank.