Set of 4 filters Size: 12.5cm from the outer circle and 3.5cm from the inner circle Replace it every 2-4 weeks Provides fresh, clean water to your lovely pets Activated carbon filter removes bad tastes and odors from drinking water < p>Feature Fountain Filters is best for Fountain Activated carbon removes odors and impurities Ion-exchange resin softens tap water to help prevent urinary tract disease Nets filter out odors and impurities hair, sediment and debris Specifications Material: Cotton + Activated Carbon Size: 12.5φ*0.8cm Inner circle diameter: 35mm Note Rinse the filter thoroughly and immerse it in water for 10 minutes before using .Replace filter every 2-4 weeks to maintain water freshness.