Fangrui Product Details 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. Adjustable Double Hole Car Spark Plug Tester Detector Ignition Plug Analyzer Diagnostic Tool Car Spark Plug Tester Detector With Dual Hole Advantage: 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. Usage: Test Spark Plug Performance And Ignition Strength Application Range: 12v Gasoline Vehicles Car Spark Plugs Car Spark Plug Tester Using Note: 1. Please Turn Off Power Before You Place Spark Plug 2. The Spark Plug Tester Is A High-voltage Detector, So Do Not Touch Spark Plug With Hand At Work To Avoid Danger. Car Spark Plug Tester User Manual: 1.place The Spark Plug Into Tester Hole 1 Or 2; If You Want To Compare The New Spark Plug A