Which of the following describes the nominal size concept for manufacturing parts?

• A. Actual size
• B. Nominal size with tolerance
• C. Exact size
• D. Guaranteed size

Answer: (B)

Nominal size with tolerance describes a target dimension used in design and the allowable variation around that target. Designers pick a nominal size so everyone talks about the same reference, but real parts can deviate a little during manufacturing. The tolerance defines how much deviation is acceptable, so the actual size should fall within that specified range. For example, a shaft with a nominal diameter of 20 mm and a tolerance of ±0.05 mm can be 19.95 to 20.00 mm, and a mating hole with its own tolerance will combine to determine whether a proper fit results. This approach reflects manufacturing realities: you aim for a target, but require acceptable limits of variation to ensure parts still assemble correctly. The other concepts—actual size (the measured dimension), exact size (zero tolerance), or guaranteed size (not a standard term)—do not capture the idea of targeting a dimension with an allowed range.