297 Chapter 8 Position Tolerancing Fundamentals Copyright Goodheart-Willcox Co., Inc. size for two holes. Therefore, it gives the position tol- erance for both of the holes. The other feature control frame is placed adjacent to the noted size for the three-hole pattern. This feature control frame speci- fi es the position tolerance for each of the three holes. Both feature control frames in the given fi gure have a diameter symbol in front of the tolerance value. A diameter symbol in the tolerance speci- fi cation indicates the shape of the tolerance zone (cylindrical). Omitting the diameter symbol would result in an unspecifi ed shape of the tolerance zone and would be incorrect for the tolerance application method shown on the given part. The decision of what shape to specify for a position tolerance zone is based on the functional requirements for the toleranced feature. Holes are typically given round (cylindrical) tolerance zones. Width features such as slots and tabs are usually given rectangular tolerance zones. Position tolerance feature control frames may consist of a single segment or multiple segments. The composition of the single-segment (single-line) position tolerance feature control frame defi nes the tolerance zone shape and size. It also defi nes the datum reference frame to which the tolerance zone must be located and oriented. Multiple single-segment (two-line or three-line) and composite position toler- ance feature control frames are more complex. They are explained in the next chapter. Position tolerances include an implied RFS material condition on the tolerance value if no material condition modifi er is shown. When a mate- rial condition other than RFS is to apply, either the MMC or LMC modifi er must be shown. A mate- rial condition is always applicable, either implied or specifi ed, because position tolerances are only applied to features of size and bounded features. Maximum material condition (MMC) and least mate- rial condition (LMC) modifi ers indicate the tolerance zones vary according to the produced feature size. The correct use of MMC and LMC modifi ers can signifi cantly improve the producibility of the parts. Feature Control Frame Information shown in a position tolerance fea- ture control frame must be shown in the correct sequence. See Figure 8-3. The geometric characteris- tic symbol (tolerance symbol) must be shown fi rst. It is followed by the tolerance value, and then by the datum feature references. Feature control frame Datum feature symbol Basic dimension Goodheart-Willcox Publisher Figure 8-2. Basic dimensions, datum features, and position tolerance specifi cations are required to completely defi ne position tolerance requirements. Metric Inch Goodheart-Willcox Publisher Figure 8-3. A position tolerance feature control frame may be used for inch or metric tolerance values.