FIG. 1 is a bottom plan view of a slider for zipper fasteners, showing my new design; FIG. 2 is a front elevational view thereof; FIG. 3 is a top plan view thereof; FIG. 4 is a side elevational view thereof from the right of FIG. 2; FIG. 5 is a side elevational view thereof from the left of FIG. 2; and, FIG. 6 is a rear elevational view thereof.