Features: 1. Fitment: Suitable for gasoline engines with M14 or M12 spark plugs. The tool joint must be installed in the position of the spark plug 2. Keep Valve Closed: Pressurizes the cylinder to help hold valves closed with compressed air. This allows the valve's oil seal to be replaced without the need for dismantling. 3. Testing Usage: When the cylinder is under compression stroke. If the air tightness of the engine is not good enough, you can hear constant air leakage. Diagnose damaged parts by listening for leak locations. 4. Widely Used: Suitable for cars, trucks, ships, motorcycles, ATV and other gasoline engines. Not applicable to diesel engine vehicles 5. Sturdy: Air valve holder pressure tubes are made of robust piping and corrosion resistant joints to prevent wear and high pressure and ensure long term reliable use. Specification: Item Type: Engine Air Valve Holder Thread: M12/M14 Compressed air (working pressure 30psi110psi) Air Intake: 1/4in quick coupler male plug Fitment: Suitable for gasoline engines with M14 or M12 spark plugs. The joint of this tool must be installed in the position of the spark plug