I claim the ornamental design for an adjustable draw bar for trailer hitches, as shown and described.
FIG. 1 is a rear perspective view of an adjustable draw bar for trailer hitches showing my new design.
FIG. 2 is a front elevation view.
FIG. 3 is a rear elevation view.
FIG. 4 is a right elevation view.
FIG. 5 is a top plan view; and,
FIG. 6 is a bottom plan view.
The broken lines, in FIGS. 1 through 6, depict environmental structure associated with the design in a condition use. The broken lines and structures they depict form no part of the claimed design.