Which statement describes the relationship between datums and tolerances?

Datums are key references in geometric dimensioning and tolerancing that establish a framework for measurement and manufacturing. They define the specific locations and orientations from which other geometrical features are derived and measured. The statement that datums define the limits of tolerances accurately reflects the role of datums in GD&T.

In practice, a tolerance specifies how much a feature can deviate from its true position or form. However, without datums, those tolerances would lack a defined reference point. Datums provide the necessary framework for establishing the permissible variations of the features associated with them. Tolerances are thus linked to datums, as they determine how tightly or loosely a feature can exist in relation to its datum reference frame.

This relationship is crucial in ensuring that parts fit together correctly in assembled products, as it helps control the functional requirements of the components. Understanding the hierarchy and interaction between datums and tolerances is fundamental to ensuring effective design and manufacturing practices, making option B the correct assertion about their relationship.