The subject of consideration in this article is the process of modeling the dimensional relationships at the Assembly stage using a single-circuit graph size scheme, which describes the mechanism of the individual parts of the conjugation in the implementation of the Assembly area group interchangeability methodology, reflecting the specific conditions of production. In the context of dimensional modeling, calculation procedures are considered on the basis of the developed mathematical model, which can be applied to both single-circuit and multi-circuit size schemes with dependent size chains. In particular, for the conditions of large-scale production, the algorithm for determining the scattering field of the assembled parts sizes by sorting them into size groups is considered. The design procedure is considered on the concrete example which describes a variant of completing of details with rather wide tolerances in the Assembly unit meeting the set criterion of working capacity.