The ornamental design for a dual sided nailfile, as shown and described.
FIG. 1 is a perspective view showing my new dual sided nail file design;
FIG. 2 is a top view showing my new dual sided nail file design;
FIG. 3 is a side view showing my new dual sided nail file design;
FIG. 4 is a bottom view showing my new dual sided nail file design;
FIG. 5 is a front end view my new dual sided nail file design; and,
FIG. 6 is a rear end view showing my new dual sided nail file design.
The broken lines immediately adjacent the shaded areas represent the bounds of the claim and all other broken lines are for illustrative purposes only. None of the broken lines form a part of the claimed design.