You don't need an actual test tube unless you want to hold water. It can hold dry or fake plants with the printed tube (or with no tube). I would recommend using tree supports when printing. It fits a 25mm tube or 1" (scale to 102%). I bought some generic ones a while back but any will do. I included the .step if you'd like to attempt to modify/scale it to fix whatever size you've got. Happy printing! Feel welcome to leave a make.