This 3u 3x1 Gridfinity bin holds the four allen wrenches that were included in the Elegoo Centauri Carbon tool kit that came with your printer.  It holds them flush so they can be stacked on, and includes a finger recess so you push on the end of the wrenches and they'll pop up for easy removal.  It also includes a hole for them so you can easily store them while in use.