Which tolerance would be used to ensure straightness in a manufactured part?

Form tolerance is the correct choice for ensuring straightness in a manufactured part because it specifically measures the shape and geometric characteristics of the part itself, independent of its location or orientation. Straightness is a type of form tolerance that defines how much a line or surface can deviate from an ideal straight line. By applying form tolerance, manufacturers can guarantee that certain features of the part maintain a straight profile, which is crucial for fitting, assembly, and overall functionality.

The other types of tolerances, while important in their own right, focus on different aspects of manufacturing. Orientation tolerances relate to how features are positioned relative to each other, location tolerances deal with the exact placement of features in space, and profile tolerances describe the outline of complex shapes. Thus, when the aim is to control straightness, form tolerance is the most applicable measure.