This Electric Solenoid (air valve) are used with air horns are for both 12 volt and 24 volt vehicles . When the vehicle's horn button is depressed, the Solenoid becomes electrically energized, opening its chamber and permitting air to reach the horn. The solenoid remains engaged as long as the horn button is depressed. Max 150 PSI. Threaded air outlet screws in to any horn that has a 1/4" female thread, and the compression air inlet side will accommodate a 1/8" outer diameter hose.