The ornamental design for a grillbrushattachment having three rows of bristles, as shown and described.
FIG. 1 is a rear isometric view of a grill brush attachment having three rows of bristles in accordance with the new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a top view thereof;
FIG. 5 is a bottom view thereof; and,
FIG. 6 is a side view thereof.
The broken lines shown on the side of the grill brush attachment in FIGS. 1 and 6 and the horizontal broken lines shown on the attachment in FIG. 5 represent the bounds of the claim while the broken lines showing bristles extending from the top of the attachment illustrate a portion thereof. All of the other broken lines are understood to illustrate the environment in which the article embodying the design is used. None of the broken lines form part of the claimed design.