Pet lower urinary tract health maintenance filter, compatible with all types, usable for 30 days. - Product Name: Absorbent filter for lower urinary tract health maintenance - Quantity: 4+1 pieces ⇒ 4 pieces as one has been opened - Filter Type: Compatible with all types - Usage Period: 30 days - Purpose: Pet filter Thank you for viewing. I am selling this because my cats didn't like it. It's a set of 5, but I've opened one, so I'm offering 4 pieces.