Upgrade your tractor or trailer with the Indigo Blue Deluxe Screw-On Aluminum Air Valve Knob With Stainless Plaque. This large screw-on knob features an indigo blue finish and a stainless steel plaque, adding a touch of style to your vehicle. It fits most makes and models and is sold individually. This air valve knob is practical and easy to install, making it a great addition to your vehicle.