In bilateral types of tolerance, Feature Dimensions are allowed to vary on both sides of the basic size. In other words, the tolerance limit lies on both sides of the basic dimension. For example, if a hole basic size is 20 mm and it’s value can vary from 19.8 mm to 20.1 mm. This type of tolerance is known as Bilateral tolerance.

Bilateral Tolerance system is recommended for parts to be mass produced. In this system, the operator always targets for the basic size.