What is the purpose of MMC in relation to position tolerances?

• A. To enforce identical sizes for all holes.
• B. To reduce the tolerance zone regardless of size.
• C. To set a fixed, unchanging tolerance regardless of size.
• D. To permit a bonus tolerance when actual size approaches LMC for holes or MMC for shafts, affecting the position tolerance.

Answer: (D)

The idea behind MMC in relation to position tolerances is to allow a bonus in the positional tolerance based on how far the actual feature size is from its most restrictive material condition. For holes, when the hole size moves toward the largest allowed (toward the least material around the hole), you get extra latitude in how far the axis can be from its true position. For shafts, when the size moves toward the largest allowed (toward MMC), you also gain that additional allowance. In other words, the position tolerance isn’t fixed; it expands as the size of the feature approaches the less restrictive extreme, making it easier to assemble parts without violating the tolerance.

This explains why a MMC modifier can increase the permissible positional error beyond the basic tolerance, reflecting that more misalignment can be tolerated when the feature size itself is more permissive.