The ornamental design for a threetierriser, as shown and described.
This patent contains at least one drawing/photograph executed in color. Copies of this patent with colored drawing(s)/photograph(s) will be provided by the Office upon request and payment of the necessary fee.
FIG. 1 is a top perspective view of a three tier riser, showing my invention.
FIG. 2 is a front elevational view of the invention shown in FIG. 1.
FIG. 3 is a rear elevational view thereof.
FIG. 4 is a top plan view thereof.
FIG. 5 is a bottom plan view thereof.
FIG. 6 left side elevational view thereof.
FIG. 7 is a right side elevational view thereof; and,
FIG. 8 is a right-side perspective view showing only the bottom single tier of the riser.