A cross between a sandbag, kettlebell, medicine ball and dumbbell. The active movement of the steel shot inside the bell is great for simultaneously challenging your muscles, working your core, and pushing your stamina. The outer shell is made from a tough, stretchy neoprene, which will enable you to engage hand and wrist gripping muscles.The difference between the SandBell and the SteelBell is the density and size per weight. The diameter of a 4lb SandBell is nine inches, and a nine inch diameter SteelBell weighs 10lb. The shifting steel shot inside the SteelBell moves much faster than sand, increasing instability and grip characteristics.