5 PACK - 4" x 14" 200 Micron Aquarium Sump Polyester Felt Sock Filter for Freshwater and Saltwater Made in USA Filter Socks Improve Water Quality with 200 Micron Filtration Made in USA with high quality materials Fits any 4" diameter sock holder - especially the ones we sell! Easy to clean and last a long time 5 Pack. Buy one time for continued micron filtration!