Series 550 is a safety coupling that feature an easy-to-grip design with a fully automatic function. They are smaller, much more compact and generate higher flow than comparable designs. It is a one hand operated safety coupling that vents before disconnection, eliminating the risk of hose whip.Series 550 is a safety coupling that feature an easy-to-grip design with a fully automatic function. They are smaller, much more compact and generate higher flow than comparable designs. It is a one hand operated safety coupling that vents before disconnection, eliminating the risk of hose whip.