The ornamental design for a drillhead for wallanchor device, as shown and described.
FIG. 1 is a perspective view of a drill head for wall anchor device showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a left side elevational view thereof; and
FIG. 7 is a right side elevational view thereof; and,
FIG. 8 is a perspective view thereof, the wall anchor device depicted by means of broken lines being for illustrative purposes only and forming no part of the claimed design.