Shop reliable and long lasting pre- and post-inline water filters. Easy to install for undersink, refrigerator, and bathroom applications. Most in line water filters come with 1/4" or 3/8" female threads and install on the water lines using fittings. To install an inline filter without fittings, look for filters that utilize quick connect fittings (QC) or John Guest fittings (these are also known as push to connect fittings). If your refrigerator doesn't come with a refrigerator water filter you can install an inline water filter on your refrigerator water line. Because they can be used in a variety of applications, inline filters are often referred to as universal water filters.