A dumbbell is a piece of weight training equipment which are considered a type of free weight. Actually, dumbbell is a weight held in one hand. Therefore, dumbbells are usually used in pairs.
Dumbbells are divided into two types:
1. Adjustable dumbbells (they consist of 35 cm long steel bars with diameter of 25 cm and look like miniature barbells). The central part is engraved with a crosshatch pattern to enable sportsmen get a good grip. There are iron weight plates (from 1 to 40 kg) placed on outer sides of the dumbbell helping to obtain the desired total weight. These weights are secured with clips or collars. The "spinlock" dumbbell has threaded outer portions, and the collars are large nuts that screw on and secure the plates through friction.
2. Fixed-weight dumbbells are weights designed in the shape of a dumbbell. They usually consist of cast iron coated with rubber to avoid injuries. There are also cheaper versions that comprise of a rigid plastic shell filled with concrete.
Due to their flexibility, dumbbells can be used in all types of weight training, but the most popular dumbbell exercises will always be the Biceps curl and the Bench press. It is necessary to wear weightlifting gloves when using dumbbells to avoid calluses on the palm of the hand. Although they are not detrimental to weight training, but some sportsmen dislike them and use leather gloves.