The SDRC Series of dumbbells combines one-piece cast heads with steel inserts, bolted onto the handle. Then the bolt is welded to secure the head for extra durability and safety. The SDRC dumbbells will never rotate like the conventional dumbbells on the market. CAP's one piece design offers many benefits. The SDRC Series are smaller than conventional dumbbells and accurate in weight. Furthermore, molded end caps with numbers permanently marked prevent stickers from coming off during use.