This is a laser-cut cube for standing up test tubes and centrifuge tubes of various sizes. It will accommodate 16mm test tubes or centrifuge tubes (like 15ml tubes), 1.5 ml tubes, and tiny .2ml PCR-type tubes.
This is a design for laser cutter and intended to be cut into 3mm wood. Since I use K40 Whisperer for lasering on a cheap-Chinese laser cutter (awesome!), this is a basic Inkscape SVG file, which works great with that amazing tool (thanks Scorch Works!)
I designed it, for no particular reason, to be the size of a standard Rubik's cube.