Flexible plastic zipper slider with rigidizing structure for assembly with profiled plastic zipper

A plastic slider for straddling a profiled plastic reclosable fastener particularly suited for plastic-film bags for opening and closing the fastener, the slider being constructed for assembly with the fastener by transverse movement, the slider comprising a support member having a separator finger depending therefrom for insertion between the profiled elements of the reclosable fastener, a pair of sidewalls depending from the support member and located on opposite sides of said separator finger, said sidewalls having at the lower ends thereof inwardly extending shoulder structures, said sidewalls diverging outwardly in an uninstalled slider so that said inwardly extending shoulder structures are spaced apart a distance adequate for transverse installation of the slider over the profiled elements of the reclosable fastener without interference, and rigidizing means on the slider to move the sidewalls into and retain them in an assembled position on the fastener whereby said shoulders cooperate with the bottom of the reclosable fastener to prevent the slider from being lifted off the fastener while the slider straddles the fastener.