This paper proposes a scheme for the tolerance-specification that uses the features' function information and mating condition attributes in the assembly to derive an appropriate tolerance specification as per the design intents. The proposed mirror method provides a way to locate the critical components. It helps the user identify functional features and group them into clusters. Temporary DRF (Datum Reference Frame) is first generated for each cluster of features on critical components by selecting specific features as datum features. Other features (that are not datum features) present in the same cluster are then toleranced with respect to those datum features. The temporary DRFs as well as the tolerancing scheme are then copied (a mirror image of the critical component) to the other mating components (which are mating with the particular critical component). The final DRFs on the critical components are then decided by analyzing the temporary DRFs and the given functional requirements of each component. Appropriate geometric tolerance types and material conditions for toleranced features are generated following the standards and the industrial practices.