The ornamental design for a screwdriver bit head, as shown and described.
FIG. 1 is a fragmentary perspective view of a screwdriver bit head showing my new design;
FIG. 2 is a fragmentary side elevation of the screwdriver bit head as viewed from the right in FIG. 1, the opposite side elevation being a mirror image thereof;
FIG. 3 is a fragmentary side elevation of the screwdriver bit head as viewed from the right in FIG. 2, the opposite side elevation being a mirror image thereof;
FIG. 4 is a top plan view of the screwdriver bit head as viewed from the top in FIG. 2; and,
FIG. 5 is a bottom plan view of the screwdriver bit head as viewed from the bottom in FIG. 3.