To accurately measure the small gap between relay contacts, which tool is the most suitable?

The feeler gauge is specifically designed for measuring small gaps and clearances, making it the most suitable tool for determining the spacing between relay contacts. This tool consists of a set of thin metal blades, each with a specific thickness, which can be inserted into the gap to find the exact distance. This level of precision is crucial in electrical applications to ensure that relays function correctly without improper contact or excessive wear.

In contrast, while calipers and micrometers also provide measurements, they are generally better suited for measuring the dimensions of objects rather than small gaps. A ruler, on the other hand, lacks the precision required for such small measurements and is not an appropriate choice for determining the exact spacing of relay contacts. Overall, the feeler gauge's design and purpose make it the best option for this specific task.