Dual Hole Car Spark Plug Tester Detector have two testing holes, you can test two spark plugs meanwhile and and if you suspect any spark plug works improperly you could compare and test to make accurate judgment.To Test spark plug performance and ignition strength, apply to 12V Gasoline vehicles car spark plugs.Adjustable double hole car spark plug tester detector Ignition Plug Analyzer Diagnostic ToolCar Spark Plug Tester Detector with Dual Hole Advantage:Dual Hole Car park Plug Tester Detector have two testing holes, you can test two spark plugs meanwhile and and if you suspect any spark plug works improperly you could compare and test to make accurate judgment.Usage: Test spark plug performance and ignition strengthApplication Range: 12V Gasoline vehicles car spark plugsCar Spark Plug T.