272 Machine Trades Print Reading Copyright Goodheart-Willcox Co., Inc. plane or axis. A parallelism tolerance applied to a sur- face establishes a tolerance zone defined by two par- allel planes that are parallel to a datum feature. See Figure 15‑26. The surface must lie within the toler- ance zone. Position Tolerances Position tolerances define the allowable location vari- ation of features. A position tolerance establishes a tolerance zone within which the center point, axis, or center plane of a feature of size is allowed to vary from the true (exact) position. Basic dimensions are used to define the true position of a feature in relationship to datum features. Orientation Tolerances Orientation tolerances are applied to control allowable variations in the orientation of features. Orientation refers to the angular relationship of a feature relative to one or more datum planes or datum axes. Orientation tolerances control angularity, perpendicularity, and parallelism and are applicable to surfaces and features of size. An orientation tolerance is used when other tolerances do not provide the necessary extent of con- trol. An orientation tolerance specification must have at least one datum feature reference. Angularity Angularity is a condition of a surface, center plane, or axis that is at a specified angle (other than 90°) to a datum plane or datum axis. An angularity tolerance applied to a surface establishes a tolerance zone defined by two parallel planes that are at a specified angle to a datum feature. See Figure 15‑24. The surface must lie within the tolerance zone. A basic dimension is used to dimension the angle and does not have a tolerance applied to its value. Perpendicularity Perpendicularity is a condition in which a surface or axis is at a right angle (90°) to a datum plane or datum axis. A perpendicularity tolerance applied to a surface estab- lishes a tolerance zone defined by two parallel planes that are perpendicular to a datum feature. See Figure 15‑25. The surface must lie within the tolerance zone. Parallelism Parallelism is a condition in which a surface or axis remains the same distance at all points from a datum Drawing Interpretation .003 tolerance zone Goodheart-Willcox Publisher Figure 15-24. Angularity of a surface. Boundary of tolerance zone and datum surface are perpendicular Drawing Interpretation .003 tolerance zone Goodheart-Willcox Publisher Figure 15-25. Perpendicularity of a surface.