ONLY Compatible with Catit brand fountain, will NOT fit other brands. (Check shape and product dimensions). Compatible with Catit Design Senses Fountain, Catit Flower Fountain, Catit Senses 2.0 And Catit Fresh & Clear Stainless Steel. NOT COMPATIBLE with the Catit Mini Fountain. Diameter of is about 5.75 inch. Diameter of hollow circle is about 1.5 inch. Thickness is about 0.6 inch. Triple Filtration System: Composed of a cotton layer, activated carbon and an ion exchange resin. Effectively to filter hair, heavy metals, keeps water fresh and improve the taste of the water. To prevent the activated carbon dust from shedding into water, please soak the cat fountain filter in water for 10 minutes then rinse thoroughly under running water before using. 1 to 2 weeks in summer and 2 to 4 weeks in winter. If multiple cats are using the fountain, more frequent replacement will be necessary. 6-pack of premium pet fountain replacement filters, individually packaged and sealed to maintain high quality. Enough supply for 1.5 to 6 months of use.