What is the definition of bilateral tolerances in engineering?

Bilateral tolerances in engineering are defined as a method that employs both positive and negative deviations from a specified dimension. This means that a tolerance zone is established above and below the target dimension, allowing for variation in both directions.

For example, if a part is specified to be 10 mm with a bilateral tolerance of ±0.5 mm, the acceptable dimensions would range from 9.5 mm to 10.5 mm. This approach is utilized to ensure that parts can fit and function properly while also accommodating slight variations in manufacturing processes.

The reason this method is particularly useful is that it provides flexibility during production, helping to achieve the intended functionality while recognizing that perfect precision is challenging to maintain. It allows manufacturers to produce parts that meet performance standards without necessitating precise measurements for every single part, thus balancing manufacturability and usability.

In contrast, methods that use only plus or only minus deviations (as suggested in the other answer choices) restrict the tolerance zone to one side of the specified dimension, which may be impractical for many applications. A method that allows for wide variations does not accurately define bilateral tolerances, since this specific approach focuses on well-defined limits rather than an unrestricted range.