Which tool measures the air gap between two solids using a steel leaf?

The tool that measures the air gap between two solids using a steel leaf is a feeler gauge. A feeler gauge consists of a set of thin, flat strips of steel, which are known as leaves. These leaves come in various thicknesses, allowing the user to measure small gaps or spaces with precision. When trying to determine the air gap between two solids, the appropriate thickness of the feeler gauge leaf can be inserted into the space to provide an accurate measurement.

In practical applications, feeler gauges are widely used in areas such as automotive mechanics and machining, where precise gaps are critical for the performance of moving components. The use of the steel leaf in this context ensures durability and retains accuracy even under different environmental conditions.

Other tools listed may not be designed specifically for measuring gaps in the same manner. For instance, a micrometer measures small distances or thicknesses but is not typically used for gaps between solids in the same way. Calipers can measure external and internal dimensions as well as depths, but they do not use steel leaves specifically for gap measurements. The Vernier scale is a method of taking precision measurements but is not a standalone tool like a feeler gauge for checking air gaps.