Set of 3 boxes. 4 months x 3 boxes = 12 months worth Since there are only 3 boxes left, if one box is sold, I will have to cancel the order due to insufficient stock. [Health Maintenance] This water-softening filter is designed to maintain the health of your cat's lower urinary tract. By softening the water, it supports urinary tract health. [Compatible Models] Compatible with various filters of 1.5L, 2.5L, 3L, and 3.5L, and can be used in various cat water dispensers. [Antibacterial Properties] Antibacterial polymer is used to provide clean water. Usable for about 4 months, making it economical. - Brand: Pure Crystal - Product Name: Water Softening Filter - Quantity: 4 pieces - Usage Period: Approximately 4 months - Compatible Models: Compatible with 1.5L, 2.5L, 3L, and 3.5L filters - Features: Helps maintain lower urinary tract health - Antibacterial Properties: Uses antibacterial polymer There may be changes from Rakuraku Mercari delivery to Yu-Yu Mercari delivery. Shipping is not available on weekends and holidays. Water-softening filter (4 pieces) ideal for maintaining lower urinary tract health. - Quantity: 4 pieces - Filter Type: Water-softening filter - Purpose: Maintaining lower urinary tract health Thank you for viewing.