Chapter 7 Orientation Tolerances 285 Copyright Goodheart-Willcox Co., Inc. Parallelism of an Axis A parallelism tolerance can be used to specify a parallelism control for a feature axis relative to a datum plane. This control establishes a tolerance zone defined by two par- allel planes oriented parallel to a datum plane and within which the feature axis must lie. For example, the axis of a hole can be controlled with a parallelism requirement relative to a datum plane. When a positional tolerance is applied, the feature axis must also be within the specified positional tolerance zone. In Example 7-4, positional and parallelism controls are combined using a feature control frame consisting of two seg- ments. This is known as a multiple single-segment feature control frame. A multiple single-segment feature control frame has a geometric characteristic symbol displayed in each segment, each with its own tolerance and datum feature reference(s). SECTION A-A Orthographic View Meaning 0.2 Wide parallelism tolerance zone Possible orientation of feature axis Datum plane A Goodheart-Willcox Publisher Example 7-4. Specifying parallelism of an axis relative to a datum plane.