Chapter 7 Orientation Tolerances 293 Copyright Goodheart-Willcox Co., Inc. Perpendicularity of an Axis A perpendicularity tolerance can be used to specify a perpendicularity control for a feature axis relative to a datum plane or datum axis. A perpendicularity tolerance specified to control a feature axis can establish a tolerance zone defined by two paral- lel planes perpendicular to a datum plane or axis within which the axis of the feature must lie. In this application, the datum feature is established and the feature control frame appears below the diameter dimension for the feature of size. This control only applies to the view in which it is specified. RFS is default unless MMC or LMC is specified in the feature control frame after the geometric tolerance. For example, the 0.2 wide perpendicularity tolerance zone in Example 7-11 controls the orientation as shown in Section A-A, but not in the direction represented by Section B-B. A cylindrical perpendicularity tolerance zone can be specified by placing a diam- eter symbol in front of the geometric tolerance in the feature control frame. As shown in Example 7-12, the axis of the ∅12 hole is contained within a cylindrical tolerance zone perpendicular to datum axis A. However, nothing keeps the cylindrical tolerance zone from rotating around datum axis A if the feature is viewed from the end of the ∅25 cylinder. In Example 7-12, the ∅25 cylindrical feature establishes datum axis A. This is the axis that establishes the resistance for the degrees of freedom of the part. When look- ing at the end of the ∅25 cylinder, the cylinder resists movement in the Y and Z direc- tions and resists rotation about the Y and Z axis, but there is no resistance about the X axis. Here, the effect of applying a cylindrical tolerance zone to the ∅12 hole does nothing to control the degrees of freedom of the part.