I claim the ornamental design for an oil brush, as shown and described.
FIG. 1 is front elevation view of the oil brush showing my design, wherein back, side and opposite side views are identical, showing bristles in broken lines.
FIG. 2 is a top plan view thereof, showing bristles in broken lines;
FIG. 3 is a greatly reduced exploded front elevation view thereof, showing bristles in broken lines; and,
FIG. 4 is a reduced perspective view thereof, showing bristles in broken lines.
The broken lines in FIGS. 1–4 are presented for illustrative purposes and form no part of the claimed design.