EXHIBIT 21 SUBSIDIARIES The following lists all significant subsidiaries and affiliates of A. O. Smith Corporation. Certain direct and indirect subsidiaries of A. O. Smith Corporation have been omitted because, considered in the aggregate as a single subsidiary, such subsidiaries would not constitute a significant subsidiary. Jurisdiction in Which Name of Subsidiary Incorporated AOS Holding Company Delaware A. O. Smith Harvestore Products, Inc. Delaware A. O. Smith International Corporation also d/b/a A. O. Smith Automotive Products Group-Japan Delaware AgriStor Credit Corporation Delaware Sceptor Finance Company Delaware Smith Fiberglass Products Inc. Delaware Claymore Insurance Company, Ltd. Bermuda A. O. Smith Enterprises Ltd. also d/b/a A. O. Smith Automotive Products Company-Canada Canada AgriStor Credit Corporation Canada, Ltd. Canada A. O. Smith L'eau Chaude S.a.r.l. France A. O. Smith Electric Motors (Ireland) Ltd. Ireland A. O. Smith Holding (Ireland) Ltd. Ireland Fabricadores de Componentes de Motores, S.A. de C.V. Mexico Fabricantes de Componentes Motrices, S.A. de C.V. Mexico Fabricantes de Motores Electricos de Mexico, S.A. de C.V. Mexico Metalsa, S.A. Mexico Motores Electricos de Juarez, S.A. de C.V. Mexico Motores Electricos de Monterrey, S.A. de C.V. Mexico Productos de Agua, S.A. de C.V. Mexico Productos Electricos Aplicados, S.A. de C.V. Mexico A. O. Smith Water Products Company B.V. The Netherlands