A compression fitting is a coupling used in plumbing to connect two pipes or a pipe to a fixture or valve. These fittings are generally used on stationary connections, such as toilets, vanities and refrigerators.
Compression fittings consist of a compression nut, compression ring and the compression seat. As a pipe is slid into the ring and the seat the nut is tightened down. As the compression ring is pressed into the seat, it compresses against the pipe and nut, providing a watertight seal. The benefits of using compression fittings include not having to use a blow torch and solder to make a connection, ability to easily take them apart and ability to use them on copper or plastic piping.