✅ Filters May Be Green or Blue ✅ REPLACEMENT FILTER - Get purer, cleaner water in your pool or spa with these replacement cartridge filters compatible for Pleatco: PTL18P4-4, Unicel: 4CH-21, Filbur: FC-0121. See alternate filter names below. Filters May Be Green or Blue.✅ DIMENSIONS - Diameter: 4 5/8" Length: 8" Top: Handle Bottom: 1 1/2" MPT male Threaded.✅ MULTI PACK SAVINGS - Choose from our value savings single, double or 4 pack filter bundle. Having multiple filters on hand can help extend the life of each and protects your pool or spa because you can keep 1 filter active while cleaning the other for zero filtration downtime..✅ EASY TO CLEAN - Guardian Filtration Products are designed to be long lasting and easy to clean so you can keep your pool and spa crystal clear and safe for you and your family. Our premium filter material keeps your water clearer and is easier to clean..✅ Guardian Filtration Products has been operating out of Northwest Pennsylvania since 2003. We're committed to creating affordable, high quality pool filtration products and accessories...Click Add-to-Cart or 1-Click Buy to order your pool/spa filter cartridge today!