TYPE-SC is most popular type coupler used to connect air piping in factories and used to connect air tools with hoses etc. Both socket and plug have hose use and screw use advantages. There is also a variety of other types. The types 20, 30, 40, and Types 400and600are completely interchangeable. With one check valve built into the coupling only whereas plugs do not have any check valves. Can be advantageously used where one side of the flow system needs to be sealed on disconnection.