We claim the ornamental design for an insert pin for slide fastener, as shown and described.
FIG. 1 is a perspective view of our new design.
FIG. 2 is a front view thereof.
FIG. 3 is a rear view thereof.
FIG. 4 is left-side view thereof.
FIG. 5 is a right-side view thereof.
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The dash-dash broken lines shown in the drawings illustrate portions of the insert pin for slide fastener, the dot-dash-dot broken lines illustrate the bounds of the claim; the broken lines form no part of the claimed design.