A procedure has been developed for optimally allocating tolerances and clearances in single loop planar and spatial mechanisms for minimum cost and minimum sensitivity to parameter variations. The cost of incorporating individual tolerances and clearances using specific manufacturing processes and their overall effects (sensitivities) on the whole assembly is established for each individual part. These are then incorporated into a multicriteria nonlinear optimization procedure to obtain the best tolerance and clearance specification for a part and the best manufacturing process. The procedure is developed for use in the early design stages of an assembly to allow the design to accommodate dimensional variations occurring during overall life cycle of the mechanism. The design is made as insensitive as possible to these variations, i.e. “robust” against the manufacturing and operating variations.