The ornamental design for a zipper for pants, as shown and described.
FIG. 1 is a front view of the zipper for pants showing my new design;
FIG. 2 is an enlarged view of the encircled portion in FIG. 1;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof; and,
FIG. 7 is a back view thereof.
The broken lines shown represent unclaimed subject matter, form no part of the claimed design, and should be understood as broadly indicating merely one potential location of such zipper designs on one potential item of clothing without limitation.