A tolerance allowing variance in only one direction is known as what?

A tolerance that permits variance in only one direction is termed unilateral tolerance. This means that the dimension can either increase or decrease, but only by a specified amount in one direction. For instance, if a dimension has a nominal value with a provided positive tolerance, it will only allow for an increase to that dimension, not a decrease.

In many engineering and manufacturing contexts, unilateral tolerances are advantageous because they help ensure certain features do not exceed limits that could compromise functionality or assembly processes. This type of tolerance is vital when dealing with parts that must fit into designated spaces or interfaces, where exceeding a certain dimension may result in assembly issues.

Bilateral tolerances, in contrast, allow variance in both positive and negative directions around a nominal dimension, providing a more flexible approach. Limit tolerance refers to specific maximum and minimum dimensions but does not imply directionality like unilateral tolerances. Absolute tolerance is typically applied in contexts where a fixed allowable dimension must be maintained, focusing on specific constraints rather than direction.