40mm O.D. Test tube to suction cup adapter

thingiverse

this is a simple adapter ring for a 40mm test tube, so you can suction cup it to the wall of an aquarium. why might you ask, do you need this ring or a 40mm test tube in an aquarium? Well, if you need temporary Co2 and you want to diffuse it a 100% you can pump it into an upside down container and it will diffuse over time. I am using this setup to grow plants until my fish arrive and perhaps intermittently as needed. requires: 1x m3 nut 1x m3 x 16mm bolt suction cup I now have a dual version here: https://www.thingiverse.com/thing:3551829