Dumbbells are used to exercise all major muscle groups, including arms, chest, back, abs, legs, and core. The benefits of dumbbell exercises include muscle building, improving core strength, boosting balance, providing better bone , burning calories, increasing energy levels, enhancing overall mood, and more. Built to last, these dumbbell heads are made from ASTM A48 class 20 gray iron and joined together by a 1018 cold-rolled solid steel handle (sizes 15-120 lb) finished with a durable industrial enamel coating. The CAP original hex dumbbell weights have hex-shaped heads to prevent rolling.