We claim the ornamental design for a coupler collar, as shown and described.
FIG. 1 is a front perspective view of a coupler collar of the present invention.
FIG. 2 is a side perspective view of the coupler collar of FIG. 1, including a coupler shown in broken lines for illustrating an environment for the claimed design.
FIG. 3 is a right side view of the coupler collar of FIG. 1, with the left side view, the front view, and the rear view being identical to the right side view.
FIG. 4 is a top view of the coupler collar of FIG. 1; and,
FIG. 5 is a bottom view of the coupler collar of FIG. 1.
The portions of the coupler shown in broken lines are included for the purpose of illustrating environment and form no part of the claimed design.