Newtown - I bought from Rockford and didn't have an issue. They only have one type of appliance connector which slipped right into my Rainer's collar - just be sure to tell them you need an appliance connector and not a tee. The "pyramid" top plate also worked fine on my 8 x 12 tile it's just that the long sides will require more caulk, while the short sides line up and seal fine. For an additional $50 or something they do sell a top plate that is flat designed to fit on top of the rectangular terra cotta if you wanted to go that route. Also, they sell either .005 and .006 and their default is .006 so ask them for .005 to get the "maximum flexibility." Read flexible as: if you pull on it hard enough, it will bend! I ordered the .006 and had to get it to bend a little to go into my 45* flue collar. It literally was a matter of muscle and took a couple pulls. Re: if you damper is big enough, If you can get up to the damper, you can measure the opening OR you can get 6 inch round duct from Home Depot and see if that will fit, I believe Hogwildz did that when he did his. Best wishes!