Straightness is a valuable control when two parts in an assembly require line contact. By applying straightness, we can mark the mating surface and give it special attention during the machining process. The application of straightness control is often seen in the design and manufacturing of tubes, hydraulic sleeves, and covers that require perfect contact to withstand high pressures. For the design of pins and cylindrical parts that need to fit into bores or holes to function properly, axis straightness is utilized. By using a straightness callout, we can ensure that these parts mate correctly even at the maximum material condition.