Dumbbells are an important part of any weight training system, whether it's in a gym, a commercial exercise facility or your home. These simple exercise devices, however, come in a variety of shapes and styles, in addition to varying weights. Some are fixed weights, others have a bar with plates that can be added to change weights. They can have round plates or "hex" ends. A basic choice is rubber or iron.
Cast -iron dumbbells are molded of iron or steel. They may be cast as a single component, with either round or hex ends, or have removable plates that are fastened to a bar with some type of connector. Solid cast versions are available typically in five-pound increments. Removable plates vary in weight from 2 1/2 to 25 pounds or more and can alter the weight of the dumbbell using the same bar.
Rubber dumbbells are not really rubber. They are cast iron or steel, with a cover of neoprene or other rubber or sometimes vinyl. They can be either solid units or steel bars with removable plates. Either version can use round or hexagonal ends. Except for the protective coating, they are like cast-iron dumbbells. Some cheaper types use a concrete filling for weight rather than metal.
Rubber dumbbells are easiest on floors because their protective covering is less likely to dent or scratch floors. They also resist chipping and cracking when dropped or set down heavily. The rubber covering, however, is subject to damage from sunlight or heat. Hex dumbbells are more likely to cause floor damage than round ends or plates because they have points where the flat hex sides meet.
Iron dumbbells are the standard for heavy-duty weightlifters and body builders. They take up less space on a bar than rubber-coated versions, not a big point if you're just lifting 10 or 20-pound dumbbells, but a serious matter for heavy lifting. Adding dimension to a dumbbell changes the balance slightly which can alter the arm muscle movement.