145-175 PSI air compressor pressure switch or known as a pressure control valve. This switch has one port on the bottom for air inlet hook up, which is 1/4" female NPT. This switch is also equipped with an on and off lever and an unloader valve on the side, which is 1/4" compression if the unloader is not needed it does not need to be hooked up.  This has a 1/4" Female NPT Pipe threads which can be changed to male using a pipe nipple from a local hardware store. For technical specifications please see below.

Specifications:

• Air Inlet - 1/4" Female NPT Pipe Threads
• Unloader Size: 1/4" Compression
• Equipped with a Manual On and Off Lever
• Pressure Setting: Turns on at 145 PSI and Shuts off at 175 PSI.  (Can be adjusted slightly)

Power and Amp Rating:

• 20 Amps MAX at 120 Volt
• 12 Amps MAX at 240 Volt Single Phase
• 9.6 Amps MAX at 240 Volt 3 Phase

12 Volt Power DC

• 8.6 AMPS at 32 Volts DC,
• 3.1 AMPS at 120 Volt DC
• 1.6 AMPS at 240 Volt DC

If you have a larger industrial compressor with a magnetic starter, the amps do not matter.  All the switch is doing is telling the starter when to Turn on and Shut Off.