The ornamental design for a trailerhitchball mount, as shown and described.
FIG. 1 is a front perspective view of the trailer hitch ball mount;
FIG. 2 is a left view thereof;
FIG. 3 is a right view thereof;
FIG. 4 is a front perspective view of the trailer hitch ball mount with a notched trailer hitch ball with a bolt and a nut; and,
FIG. 5 is a front perspective view of the trailer hitch ball mount with a trailer hitch ball with a bolt, a washer, and a nut.
The broken lines depict the notched trailer hitch ball with bolt, the nut, the trailer hitch ball with a bolt, and the washer that form no part of the claimed design.