Three-layer mattress spring unit

Description

FIG. 1 is a perspective view of the three-layer mattress spring unit;

FIG. 2 is a right side view thereof, the left side view being a mirror image of the right side view;

FIG. 3 is a front view thereof, the rear view being identical to the front view; and,

FIG. 4 is a top view thereof, the bottom view being identical to the top view.

Claims

The ornamental design for a three-layer mattress spring unit, as shown and described.