Since each thickness is a different color, there’s no need to read the feeler gauge to tell your measurement. They are used to check gaps, alignment, and narrow slots. Gauges are nonmagnetic, nonmarring, noncorrosive, nonsparking, and resistant to oil.
Keep spark plugs working efficiently. These feeler gauges slide between the electrodes to measure the gap. If the gap is incorrect, they have an adjustment tool to bend the electrode where you need it.
Wire Measuring
Wire-measuring gauges measure using different wire thicknesses.