Quick connect screw couplings, with shut-off facility at both ends, are designed for hostile working environments within construction machinery. The socket and plug are connected firmly together by a hand nut with a special heavy-duty thread. The coupling is resistant to heavy pressure surges and high impulse conditions, such as those occurring in vehicle hydraulic applications. Sealing and disengagement is based on the same principle as for the screw couplings used for piping. Type 56 is identical in appearance to type 65; however, it possesses a modified interior that enables it to connect under pressure.