This is a modular stand for your 3DBenchy test prints.
The stand can be expanded horizontally and/or vertically using the "mending plates" and M3 screws (I used M3 hex socket button head cap screws). Typically I used M3x12mm or M3x14mm for the screws that go into the base plates and no longer than M3x8mm screws that go into the top of the backs to connect the next level above. There are also small clips that can be used to keep the base plates straight and not separate at the front. The clips come in large and small sizes although printing in PLA the small size typically works best. The large is provided for a slightly tighter fit.
The "tray" pieces are mirrored so they will seamlessly go side to side looking like continuous water surface if you alternate between tray A and tray B.