The ornamental design for a platform of a sprinklerbase, as shown and described.
FIG. 1 is a perspective view of a platform of a sprinkler base;
FIG. 2 is a front view of the platform of the sprinkler base of FIG. 1;
FIG. 3 is a right side view of the platform of the sprinkler base of FIG. 1;
FIG. 4 is a top view of the platform of the sprinkler base of FIG. 1; and,
FIG. 5 is a bottom view of the platform of the sprinkler base of FIG. 1.
The left side view of the platform of a sprinkler base is the same as the right side view and the rear view of the platform of the sprinkler base is the same as the front view.