Air Compressor Pressure Control Switch 4 Ports 95-125 PSI w/ 0-200 Black
It has 4 ports (¼ » female NPT), including a tank-connection port and 3 extra ¼ » ports. If your compressor does not need the unloader you can omit that connection.
Square D 135-175 PSI Air Compressor Pressure Switch, Pumptrol, Hinge Grey
The unloader is used to unload head pressure off the compressor pump for a load free start up. If your compressor does not require a unloader valve on the pressure switch you can leave it not hooked up and the switch will still function properly.