Task Group 142 Tolerances Practice Test

Unilateral tolerances let allowable variation occur in only one direction from the nominal size. That means you choose either a plus or a minus limit, but not both, so the size can move only larger than the basic size or only smaller than it.

For example, with a basic size of 10.00 and a unilateral tolerance of +0.05/0, the acceptable range is 10.00 to 10.05. If the tolerance is -0.05/0, the range is 9.95 to 10.00. This is different from a bilateral tolerance, which allows equal variation in both directions (for instance, ±0.05 would give 9.95 to 10.05). The idea of any variation without direction or fixing the dimension exactly doesn’t describe unilateral tolerancing.