Threads can center themselves in holes, but using maximum material condition allows hard gaging to verify position tolerances for threaded features. While the additional tolerance from MMC for threads is small, it legitimizes using hard gages. The example drawing shows a gage that could inspect threaded holes relative to a datum using the projected tolerance zone, with values in parentheses indicating design dimensions without gage tolerance or wear allowance.

1. Threads - MMC
There is a Place for MMC on Threads
Many people believe that since threaded fasteners generally center themselves in the
threaded hole, MMC (maximum material condition) is not applicable. MMC is needed on
threaded features to legitimize hard gaging. Granted, where MMC is applied to threads
the resulting additional tolerance (bonus) will be very small and hard to determine. Using
MMC, however, does allow the use of hard gaging to verify the position tolerance - even
when the projected tolerance zone is applied.
To the right is a drawing of a gage that could be used to inspect the projected
tolerance zone of the M10 threaded holes relative to datum A stated in the lower
of the two single segment position tolerances. The values in parenthese are the
design values for this gage based on the drawing. They do not include gage
tolerance or wear allowance. This gage is legitimate because MMC is used to
modify the tolerance.