These automatic tire deflators air your tires down to a pre-set PSI and are completely hands free! Now, you don't have to kneel in the dirt when you're airing down your tires for off-roading. Simply screw the set of four deflators on to your valve stems and walk away. They'll shut off automatically and can be set between 5 and 20 psi. They come pre-set to 12 psi.