Why is tolerance important in mechanical design?

• A. It reduces electrical resistance.
• B. It increases manufacturing cost only.
• C. It ensures parts fit together properly and function reliably without being too loose or tight.
• D. It prolongs battery life.

Answer: (C)

Tolerance defines the allowable variation in a part’s dimensions, and that range is what lets parts come together and work reliably in an assembled product. In mechanical design, you can’t make every part exactly the same every time, so you set tolerances to ensure a proper fit between components—like a shaft and bearing or a bolt and hole. If the tolerance is too tight, parts become hard to manufacture or assemble and may fail to fit in the real world. If it’s too loose, they may have excess play, misalignment, or faster wear. A well-chosen tolerance balance ensures the parts fit together properly, function smoothly, and perform consistently over time.

Other choices don’t align with the main purpose of tolerances. Tolerances don’t directly control electrical resistance or battery life, and while looser or tighter tolerances can affect manufacturing cost, the primary goal is reliable fit and function rather than cost alone.