A climbing ascender is a device used in rock climbing and mountaineering that allows the climber to ascend a rope. It consists of a metal frame with teeth that grip the rope and a cam that locks onto the frame when weight is applied. Climbing rope ascenders are typically used in pairs, one for each hand, and are attached to the climber's harness with a lanyard. Climbers use ascenders to move up fixed ropes, such as those used for hauling gear or climbing trees. They can also be used to ascend freely hanging ropes, though this is generally considered more difficult.