[Compatibility] ONLY compatible with Catit brand fountains; 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. [Round Pet Filter] Diameter is about 5.75 inches. Diameter of hollow center is about 1.5 inches. Thickness is about 0.6 inches. [Premium Quality Filters] Triple filtration system: composed of a cotton layer, activated carbon, and ion exchange resin. Effectively filters hair and heavy metals, keeps water fresh, and improves water taste. [Frequency of Replacement] To prevent activated carbon dust from shedding into water, soak the cat fountain filter in water for 10 minutes, then rinse thoroughly under running water before use. Replace every 1 to 2 weeks in summer and every 2 to 4 weeks in winter. More frequent replacement may be needed if multiple cats use the fountain. [Premium 6-Pack Pet Fountain Filters] Pack of 6 premium pet fountain replacement filters, individually packaged and sealed to maintain quality. Provides enough supply for 1.5 to 6 months of use.