Which statement correctly describes MMC for a hole and shaft?

Which statement correctly describes MMC for a hole and shaft?

• A. MMC: hole at its smallest diameter; shaft is at its largest diameter.
• B. MMC: hole at its largest diameter; shaft at its smallest diameter.
• C. LMC: hole at its smallest diameter; shaft at its largest diameter.
• D. LMC: hole at its largest diameter; shaft at its smallest diameter.

Answer: (A)

The key idea is that maximum material condition (MMC) depends on the type of feature. For holes (internal features), MMC occurs when the hole is at its smallest diameter, because that leaves the most material around the hole. For shafts (external features), MMC occurs when the shaft is at its largest diameter, because that represents the most material in the shaft. When a hole and a shaft mate, the worst-case mating condition—most material present in the interfacing region—happens with the hole at its smallest and the shaft at its largest. That’s why the statement describing the hole at its smallest diameter and the shaft at its largest diameter is the correct description of MMC for a hole and shaft.

The key idea is that maximum material condition (MMC) depends on the type of feature. For holes (internal features), MMC occurs when the hole is at its smallest diameter, because that leaves the most material around the hole. For shafts (external features), MMC occurs when the shaft is at its largest diameter, because that represents the most material in the shaft. When a hole and a shaft mate, the worst-case mating condition—most material present in the interfacing region—happens with the hole at its smallest and the shaft at its largest. That’s why the statement describing the hole at its smallest diameter and the shaft at its largest diameter is the correct description of MMC for a hole and shaft.