Randomly sized rings that can be put in most plastic test tubes.
Ants like less space. These rings turn your test tube into a mini formicarium. It also provides a much more stable humidity chamber inside the test tube. The queen will also feel safer because of the narrow entrance. A nice added bonus is that the ants will stay inside the little chambers making feeding the colony so much easier and less stressful.
You will get random inserts. This means random colors and random sizes. If your ringserts don't fit in your test tube there is nothing that can be done about it.