Material: Metal
Instruction manual:
1. Normal: The standard tire pressure， the transparent window should be green， the normal running of the vehicle.
2. Warning: The tire pressure slightly lower than the standard of about 10 percent， a transparent window yellow green， should be inflated.
3. DANGER: about 25% lower than the standard tire pressure， a transparent window should be yellow-red， should immediately check， aerated.
Steps:
1. Unscrew the existing bonnet
2. The tire pressure adjusted to the range recommended by the manufacturer. (Tires must be cold)
3. hand to instruct the cap is screwed onto the tire valve
4. Regularly check indicator cap
5. If the green drops red color indicates insufficient tire pressure
6. inflate the tire to the correct pressure
7. Keep the bonnet clean easy to check.