FIG. 1 is a perspective view of a first embodiment the swing arm of my design; FIG. 2 is a front view thereof; FIG. 3 is a rear view thereof; FIG. 4 is a top view thereof; FIG. 5 is a bottom view thereof; FIG. 6 is a left side view thereof; and, FIG. 7 is a right side view thereof. Where included, broken lines showing structure are for illustrative purposes only and form no part of the claimed design.