Some of the older Fisher stoves have a flue collar that is actually 8" outside diameter. As it is recommended to run the male end of the connector pipe inside the stove's flue collar, this sizing makes it difficult to do so. Our Fisher stove adapter is sized to go over the flue collar. Then the male end of the connector pipe fits inside of this adapter, allowing for a drip free connection. In addition, it has a formed bead to further insure that the creosote formed from combustion remains inside the pipe.