Abstract In the author’s opinion, the combined application of the preferred-numbers idea and the law of similitude provides an effective means of eliminating unnecessary variety of sizes and of simplifying tool and machinery equipment in any field of industrial production. In the application of this method to the standardization of centrifugal pumps, the author develops a set of geometric series conforming to the preferred-numbers table. The formation of the series, and their interconnection and use for treating the standardization problem, are illustrated by numerical tables, charts, and diagrams. Standardizations of hydraulic and mechanical parts of centrifugal pumps are tied together by the use of the law of similitude, resulting in the formation of a set of interconnected geometric series applicable to both cases.