GD & T – Material Condition Modifiers

What are Material condition modifiers?

GD&T on holes (and shafts) provides a powerful tool for increasing inspection yield without trial-and-error fitting or binning.
Used when the size of the feature interacts with its location.
If ⓜ the symbol appears after the tolerance, then the specified tolerance holds only at maximum material condition.
As the feature departs from MMC, the amount of departure can be added to the position tolerance.
MMC is commonly used for clearance-type applications.

This feature control frame specifies the positional tolerance zone as a circle of diameter .010 at MMC, centred according to the basic dimensions given.
The tolerance zone's size depends on the size of the hole.
- MMC of hole = .250
- LMC of hole = .255
Similarly, if Ⓛ symbol is used, the stated tolerance holds at least material condition (LMC). As the part departs from LMC, the amount of departure is added to the position tolerance.
LMC is commonly used for loose fits.
If no modifier is specified, (or ⓢ symbol in past practice) then the stated tolerance holds regardless of the material condition of the feature. This is called RFS – regardless of size.
RFS is commonly used for pressed fits.