To maintain your pet's health and well-being, regularly check your pet's watering systems' parts for replacement. This black replacement cap is designed specifically for use with the Replendish® Waterer system, in sizes medium (2.5 gals.) and large (4 gals.). To ensure a proper fit, be sure to match your pet's watering system with the appropriate product/item number for this replacement cap. The cap size measures 5 1/8" x 5 1/8" x 3 1/4"