Which tool is used to measure the clearance between a surface plate and a relatively narrow surface being checked for flatness?

The tool that is specifically designed to measure the clearance between a surface plate and a relatively narrow surface being checked for flatness is the feeler gauge. Feeler gauges are used to determine gap or clearance dimensions by inserting thin metal blades of known thickness between the surfaces. This allows for precise measurement of how flat a surface is in relation to another surface.

Using a feeler gauge, one can insert the gauge into the space and determine if the surface meets the desired flatness specifications. This method is particularly effective for measuring small gaps, making it suitable for applications where precision is critical.

While a dial gauge can measure variations in flatness, it is typically used for measuring displacement more than checking minimal clearances. A thickness gauge is designed to measure the thickness of materials rather than the gap between surfaces. An angle gauge is used to measure angles and is not suitable for flatness measurement. Therefore, for measuring clearance gaps in relation to flatness, a feeler gauge is the most appropriate choice.