With a modern design, P.I.P. Puzzle Racks are suitable to hold tubes with diameters from 11 to 28mm. Made from polypropylene, they are autoclavable, freezable, and resistant to most of the common laboratory acids and chemicals. With their unique structure, they can be used both individually and connected in groups. Having wells with different diameters on each side of the rack, tubes with different sizes and volumes can be placed inside these racks at the same time. For an easier retrieval of the tubes, they have alphanumeric grid, also available in different colors for easy classification.