Types of dumbbells

By the early 17th century, the familiar shape of the dumbbell, with two equal weights attached to a handle, had appeared. There are currently three main types of dumbbell:

- Adjustable dumbbells consist of a metal bar whose centre portion is often engraved with a crosshatch pattern (knurling) to improve grip. Weight disks (plates) are slid onto the outer portions of the dumbbell and secured with clips or collars. Shown to the right is a "spinlock" dumbbell, whose ends are threaded to accept large nuts as collars. Alternatively, a dumbbell may have smooth ends with plates being secured by a sprung collar.

- Fixed-weight dumbbells are weights created in a dumbbell shape. Expensive varieties consist of cast iron, sometimes coated with rubber for safety.[citation needed] Cheaper versions consist of a rigid plastic shell that is filled with concrete.[citation needed]

- "Selectorized" dumbbells are adjustable dumbbells whose weight is changed mechanically — for example, by turning a dial or moving a selector pin — rather than manually adding or removing plates. This can make it very easy to change the weight of the dumbbell between exercises. Such dumbbells often include stands that double as storage for the additional weights not being used for a particular exercise.