I cannot find the original item but the picture gives you an idea of how it works. Though the images specifies a top bar hive, it doesn't need to be. The item in question is available from kellybees.com. Evidently, they designed their site to be more confusing, so I cannot find the direct link. Why are all bee supplier web sites so hard to use?
I am using this setup on a bee tree right now and getting good results. I's not the one from Kelly, but something I fabbed up myself.