Possible Clues:

• Protective disc attached to a wheel
• Part of a car wheel
• Wheel cover that may be chrome-plated
• Part of wheel clamp oddly below centre
• Covering for the middle of a wheel
• A pothole may cause the loss of one
• Decorative disk on a car
• One of a car quartet
• Common place for a car's name, once
• Part of car clamp oddly below focal point