Dopow Pneumatic Quick Couplers SP Socket Nut SP-20 SP-30 SP-40 Pneumatic Quick Couplers SP Socket Nut, Pneumatic Connection Solutions: Pneumatic Fittings, Pneumatic Push in Fittings and Pneumatic Connectors. Uni-directional shut-off couplers with an automatic shut off valve built in the socket. Recommended for piping of compressed air connections.