Each of four rack sides has a different size hole so the rack can accommodate various sizes of test tubes and pipettes making this cube perfect for the laboratory or classroom. Each side measures approximately 4.25″ with all of them stable enough to be the rack bottom. Two of the six sides do not hold test tubes but are modified with a tongue-and-groove allowing multiple units to snap together and join forming as long a test tube rack needed.

Please note that in order to fit inside the hole diameter, test tubes smaller than the hole diameter need to be used. 

Hole diameters: 

• 17mm, holds up to 10 test tubes.
• 13mm, holds up to 12 test tubes.
• 11mm, holds up to 16 test tubes.
• 29mm, holds up to 4 test tubes.