Compression fittings (occasionally referred to as "lock-bush fittings") include a tapered, concave conical seat; a hollow, barrel-formed compression ring (occasionally known as a ferrule); along with a compression nut and that is threaded on to the human body with the fitting and tightened to produce a leakproof connection. They are http://garrettksclu.thenerdsblog.com/108498/valves-and-fittings-options