The ornamental design for a dropbar for a trailer hitch, as shown and described.
FIG. 1 is a front perspective view of a drop bar for a trailer hitch showing my new design in solid lines and showing in phantom lines an example of a hitch ball assembly securable to the drop bar to show the environment in which the design is associated;
FIG. 2 is a perspective view thereof, similar to FIG. 1;
FIG. 3 is a left-side, elevational view thereof, the right side being a mirror image thereof;
FIG. 4 is a rear, elevational view thereof;
FIG. 5 is a front elevational view thereof;
FIG. 6 is a top, plan view thereof; and,
FIG. 7 is a bottom, plan view thereof.
The broken lines shown in the drawings illustrate portions of the drop bar that form no part of the claim.