I know there is little benefit to applying MMC to threaded features directly. However, consider the case where a pattern of threaded holes is used as the secondary datum feature [B] with the plane in which they are located as the primary datum feature [A].
When evaluating other features on the part (Ø21 hole position tolerance or profile tolerance in the example drawing), I'd like the datum reference frame to be [A | B(M)] so that I can use a portion of the datum shift available from the mating part's Ø14 clearance holes in the part alignment.
Now, the calculation for available datum shift due to MMB modifier on the datum B feature reference is dependent on the size tolerance of the feature (irrelevant/difficult to measure for thread pitch diameter) combined with the position tolerance of the datum B features with respect to Datum A and the other features in the pattern. Refer to ASME Y14.5-2018 Paragraph 7.11.5/6 and Figure 7-22 for MMB calculation.
From 7.11.5 "The appropriate boundary is determined by the collective effects of size and any applicable geometric tolerances relative to any higher-precedence datums."
If the pattern of threaded holes (datum feature B) has a FCF of [POS | Ø2(M) | A], then the "true geometric counterpart" of datum feature B at MMB should allow an additional Ø2 of clearance. Meaning a M10 threaded hole has a Ø2 undersize true geometric counterpart.
Perhaps this is easiest to apply if we specify Datum Feature [B] as the "MINOR DIAMETER" of the threaded holes (or "MAJOR DIAMETER" for male threads). Then, in this example, we can use a pin Ø2 undersize of the drill size (8.5+/-0.1mm) that creates the minor diameter.
Have any of you used MMB on threaded datum features? Does metrology software support this case?