Universal Spark Plug Gap Tool Precision gap adjustments to account for springback Some spark plugs may spring back after you adjust the gap. To reach your target thickness, use a slightly smaller feeler gauge. For example, if you want a 0.44 mm gap, use a 0.42 mm gauge. When the plug settles, the gap will reach the desired 0.44 mm. Compatibility and fit considerations Not suitable for long reach or short reach spark plugs. Before , please verify the spark plug size to ensure compatibility. Fitment and size range Designed to fit most standard spark plugs sized from 14 mm to 16 mm, as well as 10 mm and 12 mm. It is not compatible with 18 mm thread spark plugs. 32blade feeler gauge and materials Includes a quality manganese steel feeler gauge with 32 blades. Measurement range is 0.0015 inch (0.04 mm) to 0.035 inch (0.88 mm) for precise gap adjustments. Also includes a 0.010 inch (0.25 mm) brass blade specifically designed for use with electronic ignitions. 23 use scenarios Automotive maintenance Use on vehicles with standard 14–16 mm spark plugs during routine tuneups to set accurate gaps and ensure reliable ignition performance. Small engine and equipment service Suitable for lawn mowers, generators, ATVs, and other equipment that use 10–12 mm spark plugs, enabling precise gap adjustments in field or settings. Electronic ignition applications The included 0.25 mm brass blade provides compatibility with electronic ignition systems, helping ensure accurate gap settings when precision is critical.