The ornamental design for a screwdriverbit, as shown.
FIG. 1 is a perspective view of a screwdriver bit showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8. is another perspective view thereof, wherein the broken line portions of the screwdriver bit differ from the bit depicted in FIGS. 1 through 7.
The broken lines depict portions of the screwdriver bit in which the design is embodied that are not considered part of the claimed design.