Offered here in a 2-pack, the Culligan S1A-D whole house water filter replacement cartridge is an affordably priced way to ensure your filtration system continues to serve the cleanest tasting water. For up to 4 months after easy installation, these filters will significantly reduce sediment, rust, scale, dirt and more before they can negatively impact your water quality. Designed for use with water filtration systems that use 9-3/4 in. x 2-1/2 in. cartridges.