This holder, when mounted on a wall, turns a test tube into a vase.
It's designed for test tubes with a 16 mm diameter.
Test tubes are very cheap and available online (US: http://www.lcmlab.com/16mm_OD_Test_Tubes_s/428.htm EU: http://www.brouwmarkt.nl/meten-testen-labo/laboratorium-glaswerk/reageerbuisjes-en-rekjes/reageerbuis-glas-160-x-16-mm-diameter.html ), or perhaps at your local pharmacy.
Update: The cap to hide the screw is now attached to the holder to save costs. You can detach it yourself upon arrival.