This seal or gasket is for use in any Sagan Life AquaBrick water storage container cap. It fits the flat cap that comes with the AquaBrick, the spigot cap, as well as the filter cap that is used for the AquaBrick Filter System. There is a groove cut into the seal on one side and the other side is smooth. The groove side goes down into the cap and the flat side is what you should see. (Cap is not included with this item) This seal is custom made for the AquaBrick and will not fit other brands of containers.