322 GD&T: Application and Interpretation Copyright Goodheart-Willcox Co., Inc. The projected tolerance zone symbol and the projection distance are specifi ed in a position tol- erance feature control frame to indicate the zone is projected and to give the distance that it projects. The projected tolerance zone symbol consists of the letter P inside a circle. See Figure 8-33. The symbol follows the tolerance value and any shown material modifi er. The projection distance follows the symbol. The given example shows a requirement for a pro- jected tolerance zone to extend .50″ outside the part. The tolerance zone begins at the surface of the part and extends outside the part by the specifi ed distance. A projected tolerance zone establishes no requirement for the feature location within the part. To specify a position tolerance for the feature location inside the part, a second position tolerance feature control frame may be applied without the projected tolerance zone symbol. Verifi cation of a projected position tolerance is typically achieved using the axis method. The surface method of verifi cation is diffi cult to achieve and may not be suffi ciently accurate. In the case of a projected position tolerance on a threaded hole, the surface method is not feasible. Projected Tolerance Zones in Models A projected tolerance zone is specifi ed in a model by terminating the annotation leader on the hole at the surface where the tolerance zone projects. Refer to Figure 8-33. For a through hole, this requires careful application to ensure the leader is attached at the correct surface. No other indication of projection direction is required. The heavy chain line used in orthographic views is not recommended by ASME Y14.41, but its use is not prohibited. Projected Tolerance Zones in Orthographic Views A projected tolerance zone may be specifi ed on a blind hole in an orthographic view by using the projected tolerance zone symbol and specifying the projection distance. See Figure 8-34. The feature con- trol frame is the same as the one used in a model and has the same meaning. There is no need to indicate the direction the tolerance zone projects, because only one direction is possible. In the given example, the axis of the thread must be within the specifi ed .018″ diameter tolerance zone. The tolerance zone extends from the part surface to a distance .50″ outside the surface. Where a hole passes through a part, it is nec- essary to indicate the direction the tolerance zone extends. The placement of the feature control frame in an orthographic view does not by itself indicate the direction of projection. In addition to the feature control frame, a heavy chain line is drawn adjacent to the controlled axis and extends in the direction of projection. See Figure 8-35. Another method is permitted only for ortho- graphic views. Because of industry movement toward using model-based product defi nition, this practice is not recommended. It is explained here because of past practice and possible use if needed. In this method, the projected tolerance zone symbol is shown in the feature control frame but no projection Goodheart-Willcox Publisher Figure 8-33. A projected tolerance zone is specifi ed by showing the projected tolerance zone symbol and the projection distance in a feature control frame. In a model, the feature control frame is attached on the side of the part from which the zone projects. .50 Min The projected tolerance zone lies outside the part Ø.018 Projected tolerance zone symbol Projection distance Goodheart-Willcox Publisher Figure 8-34. A projected tolerance zone is specifi ed in an orthographic view by showing the projected tolerance zone symbol and the projection distance in a feature control frame.