The central problem of the paper is grouping details in the conditions of FMS (flexible manufacturing system). The criteria for forming rational detail groups were identified and. The statistical analysis of details characteristics was based on the database of products for the electronic industry. The paper proposes a mathematical method of grouping using accumulated data on the processing objects, which employs the grouping criteria. By employing such an approach we are presented with details grouped according to normative indicators of FMS equipment loading or minimum loss on their readjustment within the group of technological adjusting for every robotic technological complex (RTC).