Anyone know the OD of rigid stainless? Especially the snout of the tee? Or I guess even just the OD of the snout of any 6" tee would be good. My thimble is 6" exactly so I'm worried that I won't be able to get the snout through to connect to the tee. I want to make sure one way or the other before I order a kit. Also I'll throw in one more dumb question ;-) Can I come to the top of my existing masonry liner(7x7 id) with the single wall 6" stainless then connect it to double wall insulated pieces to get extra height? If yes do I just get brackets to support the double wall? I need at least 3 extra feet.