The ornamental design for a screw, as shown and described.
FIG. 1 is a perspective view of a screw showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a sectional view of a portion of the view shown in FIG. 2, taken along line 8-8; and,
FIG. 9 is an enlarged view of the screw, taken from indication circle 9 of FIG. 3.
FIGS. 1-9 show features of a screw in phantom lines. These features are shown for environmental purposes and do not form any part of the claimed design. The phantom lines immediately adjacent to the solid line portions of the design form the boundary of the design, with the phantom lines forming no part of the claimed design.