Expansion fastner

A one-piece, plastic fastener for lockable engagement in an opening in a panel, said fastener comprising a stem having an inner end and an outer end, a pair of legs formed integrally with and extending from said inner end in parallelism with one another and in general axial alignment with said stem, each of said legs having an elongated arm integrally formed therewith at a juncture, said arm positioned at an acute angle relative to its leg, said arms each having a free end which terminates in an integrally formed head portion, said head portions being cooperatively engageable with one another along a plurality of bevelled edges, said bevelled edges oriented in a non-radial manner along said head portions, said head portions being swingable about said juncture and with their respective arm towards one another to form a complete head having an orifice embracing said stem, said stem and arms being drivable into said opening in said panel to locate said head against an outer side of said panel, said arms including a plurality of spaced-apart indentations for permitting bending of said arms in a predetermined manner when said stem is driven into said opening, the size of said indentations decreases as their distance from said head and along said arm increases, and serration means between said head and said stem to maintain said fastener in said lockable engagement with said panel.