Square D brand, Pumptrol air compressor pressure switch, model: 9013FHG42J59M1X 135-175 PSI with unloader control valve and On / Off switch. This pressure switch is designed for a 2 stage air compressor pumping up to 175 PSI but can be adjusted anywhere from 100-200 PSI. This switch features a built in On / Off metal lever and also a unloader located on the bottom of the switch. 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. This is an authentic Square D brand pressure switch, for more specifications see below. Specifications: Brand: Square D Pumptrol Model: 9013FHG42J59M1X Number of Pressure Sensing Connection Ports: One 1/4" Female NPT (Note: 1/4" NPT Measures About 1/2" In Diameter) Unloader Connection Port: 1/4" Compression Which Accepts 1/4" Outside Diameter Copper Or High Pressure Tubing Preset On Pressure: 135 PSI Preset Off Pressure:175 PSI Differential: 40PSI Can Be Used With Single Or Three Phase Can Be Used With 110 - 575 Volts Depending On Amperage And Phase Good Up To 15 Amps Of Continuous Current. (Note: If being used with a magnetic starter the amperage does not matter since all the main power is going through the starter not the pressure switch.)