It is expandale. Nothing is holding it together. Its just notched out. It was a quick job to show my wife I'm capable of doing it! I saw the concept and put it together quick. Next week I will be refining the idea to be neater looking and hold 8-10 bottles on each row. And I couls easily build it 4 or 5 rows high without any problem.
I will be changing the front holder to a smaller circle for the neck of the bottles and making the rear ones more shallow as it would show off the bottle a little more. I will post pictures when the second version is complete!