What does bilateral tolerance indicate in the context of measurements?

Bilateral tolerance indicates that a specified dimension can vary in both directions from a given nominal value, allowing for a range of acceptable measurements above and below that nominal value. This means that if a dimension is specified as, for instance, 10 mm with a bilateral tolerance of ±0.5 mm, the actual measurement can be as small as 9.5 mm or as large as 10.5 mm. This flexibility is important in engineering and manufacturing, as it allows for natural variations that occur during production while still ensuring that the parts will function together properly.

The concept contrasts with unilateral tolerance, where variation is permitted in only one direction (either above or below the nominal size), providing more stringent control for certain applications. It also differs from options that imply different constraints on dimensions or suggest multi-dimensional variation without specifying the principle of being centered around a nominal size.