The ornamental design for a set of plates for head support system, as shown and described.
FIG. 1 is a perspective view of a set of plates for head support system;
FIG. 2 is a side view thereof; and,
FIG. 3 is a bottom view thereof.
The set of plates for head support system is shown with symbolic breaks in its length. The appearance of any portion of the article between the break lines forms no part of the claimed design.