Festo Quick Coupling Socket. For use in conjunction with Quick Coupling Probe (FES-KS2-CK-4). Socket has push-in quickrelease on one end and M5 Threaded portion on other. Also has built in check-valve. Various M5 Threaded Festo Fittings (sold seperatly) can be mounted in Socket depending on the application and tubing size. See also: FES-CPSET. See additional photo for example.