What tool is commonly used to measure valve tappet clearance?

The feeler gauge is the most appropriate tool for measuring valve tappet clearance because it is specifically designed for this purpose. Valve tappet clearance requires precise measurements to ensure optimal engine performance, and feeler gauges come in a variety of thicknesses, allowing for accurate checks against the specified clearance tolerances.

When measuring tappet clearance, the feeler gauge is inserted between the valve stem and the tappet, and the appropriate thickness cannot exceed the specified clearance, indicating whether the clearance is within the acceptable range. This tool provides the necessary precision required for engine maintenance, as even small variances can significantly impact engine efficiency and operation.

Other tools, such as a caliper or a micrometer, can measure dimensions but are less practical for the specific task of checking tappet clearance, as they lack the thin, flat profiles necessary for this application. A tape measure, while useful for larger measurements, is not suitable for the precise level of detail required in measuring small gaps like valve tappet clearances.