320 GD&T: Application and Interpretation Copyright Goodheart-Willcox Co., Inc. condition boundaries for the hole and the counterbore and they are both located at the basic location. Counterbored Holes—Separate Position Tolerances If different diameter tolerance zones are desired for the two features, then a position tolerance spec- ifi cation may be placed by the hole callout and another by the counterbore callout. See Figure 8-29. The features act independently and may travel to oppo- site sides of their respective tolerance zone. When the MMC modifi er is included in the position tolerances, there are virtual condition boundaries for the hole and the counterbore and they are both located at the basic location. Counterbores Related to Holes Individually It is possible to reference each counterbore to each hole if, for some reason, there is a need to do this. See Figure 8-30. In this case, a position tolerance is applied to the clearance hole. If there are four holes in the hole pattern, then the position tolerance applies to all four holes. A datum feature symbol is applied to one of the holes, with a note stating 4X INDIVIDUALLY. This indicates that each hole is going to serve as a datum for its counterbore. Omission of the notation would indicate that all four holes act simultaneously to establish a datum. A feature control frame is applied to one of the counterbores showing a position tolerance that ref- erences the datum feature identifi ed on the hole. The note of 4X INDIVIDUALLY is shown adjacent to the position tolerance for the counterbore. This requires each of the counterbores to act as a single entity with its position tolerance located relative to the axis of its clearance hole. When this method is used, the calculations regarding counterbore diameter and counterbore position tolerance must take into consideration the accumulation of tolerances on the hole and the counterbore. Application to Threads Position tolerances applied to a threaded fea- ture are assumed to be applicable to the location of the pitch cylinder axis. This is because threads are self-centering on the pitch cylinder. The pitch diameter, therefore, serves as the log- ical controlling feature. The feature control frame may be placed adjacent to the thread specifi cation, or it may be connected to the hole with a leader. See Figure 8-31. In a model or an orthographic view, greatest clarity is achieved when the leader points toward the axis and terminates with an arrowhead on the object line. The notation may be placed on a plane that coincides with the surface of the part or on a plane that intersects the axis of the hole. When a position tolerance is applied to the pitch cylinder of a thread, the axis method of verifi cation must be used. The surface method of verifi cation is not possible because the pitch cylinder is a derived feature and not a surface. If it is ever necessary to apply a position tolerance to control the location of either the minor or major diameter of a threaded feature, then a notation must be placed under the feature control frame. The notation should state MINOR DIAMETER or MAJOR DIAMETER. Specifi cation of a position tolerance to control these features in place of the pitch diameter should be approached with caution because there is no certainty that the various diameters of a thread will actually be perfectly coaxial when the thread is produced. Position tolerances default to apply RFS. Where it is desired to apply a position tolerance at MMC, the MMC modifi er must be shown. Some companies Ø.030 Tolerance zone Ø.022 Tolerance zone Goodheart-Willcox Publisher Figure 8-29. Separate feature control frames may be applied to specify different tolerances for the counterbore and hole. Goodheart-Willcox Publisher Figure 8-30. To indicate that the position tolerance of each counterbore is located relative to the axis of its clearance hole, separate feature control frames may be applied. The hole is identifi ed as a datum feature, individually, and the counterbores are toleranced (individually) relative to the holes.