I claim the ornamental design for an adjustable wrench head, as shown and described.
FIG. 1 is a perspective view of an adjustable wrench head;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines shown in the drawings illustrate unclaimed portions of the article and form no part of the claimed design.