FIG. 1 is a front view of the retractor mechanism; FIG. 2 is a rear view thereof; FIG. 3 is a left side view thereof, the right side view being a mirror image thereof, FIG. 4 is a top view thereof, the bottom side view being a mirror image thereof; and, FIG. 5 is a front side perspective view of the retractor mechanism. The broken lines are for illustrative purposes only and form no part of the claimed design.