Flat-Pack Test Tube Rack

This is a flat-pack test tube holder for up to 10 test tubes. At its current size, with 20mm holes, it will hold the 18mm diameter tubes or the shorter/narrower 16mm tubes. As long as the tubes will fit in the 20mm holes and are at least 90mm tall, they will fit, but you could easily scale it up/down as needed.

It is very easy and fast to print. I've seen similar models, but my slicers had issues with the files, so I just modeled my own. You will need to print 1 bottom, 1 top, and 2 sides. There are two "top" files--one with open holes, and one with the holes enclosed for a single layer. I found the "closed holes" version stuck to the bed much better. The single layer is easy to remove with a sharp knife or a reamer.