I have a triple chimney, 2 are 13" x 13" and 1 is 9" x 13" the caps would NOT fit unless altered so the tops would not touch each other. Also you have to drill into the concrete crown or the tile flue and that was not a good idea to drill the tile flue and the concrete crown was way to low to attach to, sadly there is not a clamp type attachment. I made them work but wish I had found others