When Replacing spark plugs, ensuring that the plugs have the proper gap is critical to engine performance. With improper gapping of the spark plug you may experience loss of power, misfires, spark plug fouling, increased plug wear, or poor gas mileage. Too small of a gap may give too weak of a spark to complete the combustion process within the engine; too wide of a gap can lead to the spark plug not firing correctly, causing misfires at high speeds. Using the Pingel Precision Spark Plug Gap Tool will keep you ahead of the competition. Can use with 10mm, 12mm, 14mm and 18mm spark plugs. When rotating the knob, each line represents .0023. Made from billet aluminum and anodized black and the knob is polished stainless steel. Made In USA