The T4 Accessories Tray is designed to sit on top of all of the Tetra pieces. On the tall pieces (Tetra1 and 2) the tray adds a nice band of color to the top. The tray can fit a standard-size diaper changing pad, transforming the Tetra2 into a changing table. On the wide pieces (Tetra3 and 4) the tray is a nice way to organize items displayed on top.