A quick and easy way to see which samples are in the stack and have easy access to them without going down through the whole stack and flipping them over just to read the labels. each printed rack can hold 5. I tested the stacking and with 2 walls to save on plastic they are pretty sturdy and can stack 4 or 5 high no problem (I didn't test beyond 5).

If you do not want the tab sticking out the side the second plate is without the label tabs on the side.