Which tool is used to measure to the knuckle in vehicle suspension?

Answer: C — Square/straight edge

When assessing vehicle suspension and measuring to specific components like the knuckle, a square or straight edge is essential. This tool allows for precision measurements and alignment checks. By placing the square or straight edge against the knuckle, appraisers can accurately determine the positioning of suspension components relative to one another. This ensures that measurements taken are straight and true, which is critical in diagnosing issues related to alignment and suspension geometry. While a tape measure is useful for general measurements, it might not provide the level of precision needed for detailed suspension work. Similarly, calipers are typically used for measuring smaller dimensions or distances between parts rather than large assemblies like suspension systems. A protractor, which measures angles, does not serve the purpose of measuring linear distances in this context. Thus, the square or straight edge stands out as the most appropriate tool for measuring to the knuckle in vehicle suspension.