Our new blue gasket is an idea we should have thought of years ago. It is so simple and easy to use. It sits on the top ledge of our recently redesigned f15b fermenter. If you own a f15 fermenter only the old red g15 gasket will work on that model. The ledge on the new model f15b is one half inch wide and is the top rim of the tank. The blue gasket sits in the grove on the ledge and the lid pushes down over to seal. The new gasket is blue and is much easier to use.