In GD&T, regarding holes and shafts, which statement correctly describes MMC/LMC?

• A. For holes, MMC is the largest permissible diameter; for shafts, MMC is the smallest permissible diameter.
• B. For holes, MMC is at the largest permissible diameter; for shafts, MMC is at the smallest diameter.
• C. MMC applies only to feature width; LMC to depth.
• D. For holes, MMC occurs at the smallest permissible diameter; for shafts, MMC is the largest permissible diameter.

Answer: (D)

Maximum Material Condition means the feature contains the most material. For a hole, the most material in the part remains when the hole is as small as allowed, because a smaller hole removes less material and leaves more surrounding material intact. For a shaft, the most material is in the shaft itself when its diameter is as large as allowed, since a bigger shaft contains more material. So MMC for a hole is the smallest permissible diameter, and MMC for a shaft is the largest permissible diameter. The reverse holds for LMC: a hole at its largest size and a shaft at its smallest size. This concept also governs how true position tolerances can gain a bonus allowance as a feature size moves toward MMC.