Chapter 7 Orientation Tolerances 283 Copyright Goodheart-Willcox Co., Inc. Surface Parallelism When a surface is to be parallel to a datum plane, the feature control frame is connected by a leader to the surface, or to an extension line from the surface. Since the surface is not a feature of size, no material condition modifier is used. The actual surface must be within the parallelism tolerance zone that is established by two planes parallel to the datum. The surface must also be within the specified size limits. See Example 7-2. Tangent Plane A tangent plane is a plane that contacts the high points of the specified surface. When a tangent plane control is required, the tangent plane symbol follows the geometric tolerance in the feature control frame. A tangent plane application is used with a par- allelism tolerance in Example 7-3. When using this application, some points of the actual surface can be outside the parallelism tolerance zone, but the tangent plane must be within the parallelism tolerance zone. In this application, the orientation tol- erance does not control the form of the surface. Orthographic View Meaning 11.6 LMC 12.4 MMC Datum plane A 0.25 Wide parallelism tolerance zone Two parallel planes parallel to datum plane A Model View Possible parallelism orientation of surface Goodheart-Willcox Publisher Example 7-2. A parallelism tolerance application.