Key Points
The maximum material condition (MMC) of a feature is the smallest hole or biggest pin. An MMC modifier may be applied by placing the circle M symbol in the feature control frame behind the tolerance. This allows additional geometric tolerance as the feature’s size departs from its MMC.
The feature control frame below states that the holes must be positioned within 0.6 at the feature’s MMC. The MMC for the hole is 11.7 diameter; the 0.6 position tolerance applies at this size. As the hole departs (gets larger) from its MMC size, it is allowed additional position tolerance equal to its departure from MMC. Industry often calls this departure from MMC “bonus tolerance”. The holes could have as much as 1.2 diameter position if they are produced at their LMC size of 12.3. See table below.
The MMC modifier allows additional position tolerance as the features depart from their MMC.
Example Drawing
