Features: 100% brand new and high quality Dual Hole Car Spark Plug Tester Detector hve 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. User Manual:1. Insert the spark plug into the test hole 1 or 2; if you want to compare new spark plugs and old spark plugs, put the new spark plug in the hole 1 and the old hole 22. Connect the power3. Turn on the key switch 4 clockwise to open the tester, the indicator 3 will illuminate, and the tester is now working at 1000 rpm / min.4. Turn the key switch again to adjust the operating frequency to -5000 rpm / min. The higher the frequency, the stronger the spark intensity. 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. Only compatible with 12V car Only compatible with 12mm spark plug. Package Includes: 1x Spark Plug Tester 1x Power Adapter Specifications: Material: Metal+ABS Size: Approx.85x120mm/3.35x4.72in Type: EU, US(optional) Frequency: 1000-6000 RPM/min Output: 12V 1A DC Input: 220V AC note: 1.Please allow 1-2cm errors due to manual measurement, make sure that you do not mind before you order. 2.Due to the difference between different monitors, the picture may not reflect the actual color of the item. 3.Only compatible with 12V car Only compatible with 12mm spark plug. 4.Not compatible with European spark plug.