Silvacore Pro by Duraflue 90 degree T (requires soot collection door): 5", 6", Silver, Black.Attaches to the rear of a stove using a twin wall adaptor. On the bottom goes a soot collection door, on the top any straight or elbow. Off the top of a stove is always best though. This is a twin wall clip together chimney part used to build a new chimney. Twin wall clip together chimney can be as close as 5cm to combustible materials (7cm if passing through a sealed void). No glue or sealants required. When we say 5 or 6 we speak of internal