Adjustable dumbbells consist of a metal bar whose centre portion is often engraved with a crosshatch knurl 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. Nowadays, many commercially sold dumbbells are available with sophisticated, and easy-to-use methods for weight increments adjustments. This is meant to afford ease of use, thus preventing the need to stop workouts in order to raise or lower the weights.