ABSTRACT
With the release of ASME Y14.5-2009, the symbols that were called material condition modi‚ers in earlier revisions of the standard now have different names depending on where the symbol is used in a feature control frame. ASME Y14.52009 makes a clear, necessary and, in my opinion, long overdue distinction between these symbols based on their usage. For example, if a maximum material condition (MMC) modi¢er immediately follows the geometric tolerance in a feature control frame, it means the geometric tolerance zone may increase in size depending on the as-produced size of the feature it controls-the modi¢er affects the size of the geometric tolerance zone. Likewise, if an MMC modi-¢er immediately follows a datum feature reference in a feature control frame, it means the datum feature simulator for that datum feature is ¢xed in size and shape at the appropriate boundary-the modi¢er affects how the datum feature is simulated. Similar statements can also be said for the meaning of least material condition (LMC) modi¢ers in a feature control frame. Although the concept of regardless of feature size (RFS) has been a global default since the release of ASME Y14.5M-1994 (Rule number 2), thus making the RFS material condition modi¢er no longer necessary, the concept of RFS still applies if an MMC or LMC modi¢er is not speci¢ed. Like MMC and LMC, RFS also has a different meaning depending on where it is used in the feature control frame, whether it applies to the geometric tolerance or to the datum feature reference.
