The ornamental design for a pair of surfacedesigns for a set of billiardballs, as shown and described.
FIG. 1 is a front view showing the solid-color member of my new design for a pair of surface designs for a set of billiard balls, the broken lines showing the numeral within the number spot are for illustrative purposes only and form no part of the claimed design;
FIG. 2 is a right side view of FIG. 1;
FIG. 3 is a front perspective view of the striped member of my design, the broken line showing the numeral within the number spot being for illustrative purposes only and forming no part of the claimed design; and,