In the reading of aircraft blueprints, the term "tolerance" used in association with aircraft parts or components, is the

• A. is the tightest permissible fit for proper construction and operation of mating parts
• B. is the difference between extreme permissible dimensions that a part may have and still be acceptable
• C. represents the limit of galvanic compatibility between different adjoining material types in aircraft parts
• D. is a standard for surface finish on mating surfaces

Answer: (B)

Tolerance is the amount of dimensional variation allowed in a part as specified on a blueprint. It defines a range between the smallest and largest acceptable sizes for that feature, and the tolerance is the difference between those extreme permissible dimensions. This is why it’s the best description: tolerance captures how much size can vary and still be considered acceptable, ensuring parts will still fit and function together. For example, if a shaft is specified at 20.00 mm with a tolerance of +0.02 / -0.00, acceptable sizes range from 20.00 to 20.02 mm, a 0.02 mm tolerance. The other options describe related ideas—such as how tightly parts must fit, galvanic compatibility between materials, or surface finish—which are not the definition of tolerance itself.