I claim the ornamental design for a lock unit for a trailer pintle, as shown and described.
FIG. 1 is an exploded perspective view of a lock unit for a trailer pintle showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is rear elevational view thereof;
FIG. 4 is a right side elevational view thereof, the left side elevational view being a mirror image thereof;
FIG. 5 is a top plan view thereof, the bottom plan view being a mirror image thereof; and,
FIG. 6 is a perspective view thereof, with article shown in its environmental use.
The broken lines environment is for illustrative purpose only and forms no part of the claimed design. FIGS. 2-6 disclose the article in an assembled condition.