What tool is used to gauge and set the gap of a spark plug?

The spark plug gauge is specifically designed for measuring the gap between the electrodes of a spark plug. This gap is crucial for the spark plug to function correctly, as it affects the ignition timing and efficiency of the engine. Using a spark plug gauge allows the user to accurately measure the gap and ensure it meets the manufacturer's specifications, which helps in achieving optimal engine performance.

In comparison, while a socket wrench is utilized for installing and removing spark plugs, it does not measure gaps. A piston gauge is typically used to measure the diameter of pistons or bores, and a caliper, although capable of taking precise measurements, is not as specialized as a spark plug gauge when it comes to the specific task of setting spark plug gaps. Thus, the spark plug gauge is the most suitable tool for this precise measurement task.