2020/11/19 · TAGS: cod-tube cod-test-tube 16mm-cod-vial cod-vial. The COD Test Tube produced by Aijiren is often used for water quality testing. In order to adapt to different models and brands of machines, Aijiren has launched a multi-size COD Test Tube. The caliber is a uniform 16mm, but the sizes are 9ml, 10ml, 12ml and 15ml.