Preferred Choice Of Professionals And Hobbyists - These filter socks capture debris down to 200 microns in size. They trap micro and macro organic particles, debris, and excess fish food. Premium Quality And Reusable - Solid construction with heavy duty stitching make these socks strong and durable, allowing them to be cleaned and reused numerous times. Each sock is 4 inches in diameter by 9.5 inches long with a 4-inch diameter plastic ring on top, fitting most sump holders. Also available in a 6, and 48 packs. Time Tested - Aquarium Masters has been making aquarium supplies for 40 years, and improving with each iteration. Improved Water Quality - The interlocking felt fibers of our filter socks capture all forms of physical debris found in aquariums down to 200 microns. Regularly changing out filter socks in your aquarium will help to improve your water quality by removing debris and waste before it can break down inside your aquarium. Customer Satisfaction Guaranteed - We have expert customer support available to help you with any questions you may have.