This is a completely modular test tube rack. You have the ability to change the racks height, the diameter of the holes, and the amount of tubes it can hold. The main advantage of this design is the ability for it to fit every size of test tube, and any amount of tubes thus eliminating the need to dig for a particular size of test tube rack. Tube racks of similar size go anywhere from $10 for smaller ones to over $60+ for the larger ones. The cost of printing one of these customized racks is for around $4 for a smaller one, and a minimal amount more for very large racks. This price can further be reduced by using less than 25% infill.

A .scad file for this has been uploaded to Thingyverse. With that file you can change the parameters to make it whatever size you need.