Olympic dumbbells allow a weight lifter to lift much heavier weights than a standard weight set. The hole through which the dumbbell bar is slipped is much wider, as is the bar itself. This provides added strength for more weights. Choosing the best Olympic dumbbells starts with deciding how you intend to use them, and how often. The weights can be used on dumbbell bars or on barbells, but if you are considering using the weights only on dumbbells, you will probably only need lighter weights that can be stacked onto the bar.
Be sure to consider the collars included with the Olympic dumbbells you are considering purchasing. The collars slide onto the bar once the weights have been stacked, and are responsible for keeping the weights in place during lifting. The collar should be heavy-duty, easy to install and remove, and it should affix tightly onto the bar to prevent any movement of the weight plates. Make sure the Olympic dumbbells include several collars, since you will need one on each end of the dumbbell bar. You should have enough collars for two bars so you can lift with both arms at the same time.
The individual plates can come in a variety of weights, and you will need to assess your current fitness level as well as your fitness goals so you know what weights to purchase. Make sure to purchase more weight than you can currently lift to allow for muscle growth and improvement in lifting technique. You will not need to buy plates that are large enough for use on a barbell, unless you plan to buy a barbell in addition to the Olympic dumbbells. A barbell is a wider bar that is lifted with both hands rather than just one. If you intend to purchase a barbell as well, or you think you might buy one in the future, you will want to purchase a wider variety of weights for attachment to the bars. Otherwise, start with smaller weights; be sure to buy two plates at a time, one for each side of the bar, to keep the weight even on either side.
Make sure to find out how much weight the bar itself is rated for. This will affect how much weight you can put on the bar and still safely lift it. There should always be enough room on the bar for the collar attachment; without the collar, the weights can fall off, potentially leading to injury.