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

The thickness gauge is the appropriate tool for measuring the clearance for flatness between a surface plate and a narrow surface. This tool is specifically designed to measure small gaps or clearances with precision, making it ideal for applications where flatness needs to be verified, such as in machining or assembly processes. Thickness gauges can be very accurate and typically have features that allow them to measure the distance between two surfaces effectively.

Micrometers and calipers, while useful for measuring dimensions, do not have the specialized design that thickness gauges offer for gap measurements. They may not provide the same level of accuracy for very small clearances. Gauge blocks are used more for establishing precise lengths and can be employed in various setups but aren’t specifically intended for measuring clearance between surfaces in the same way thickness gauges are. Thus, the thickness gauge stands out as the best choice for ensuring the flatness and appropriate clearance in such scenarios.