Dual Hole 12V Car Spark Plug Tester Ignition Plug Analyzer Diagnostic Detector. JFIND JF109 adjustable double hole car spark plug tester detector Ignition Plug Analyzer Diagnostic Tool. Place the Spark Plug into tester hole 1 or 2; If you want to compare the new spark plug and old one, place new spark plug into hole 1 and the old on into hole 2.
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