These gridfinity pieces hold every kind of test tube or centrifuge tube found in my lab, using them as a modular tube rack I have optimised work flow in the lab to an insane degree. Please anyone who does lab work take these and give them a try its probably the most practical thing I have ever made.

Labeled versions are hare https://thangs.com/designer/Knowledge%20is%20Human/3d-model/Gridfinity%20modular%20tube%20rack%20%28labled%29-1087248