A
figure of eight is a simple
friction device used in for descending or
belaying in
rock climbing and
mountaineering. As the name suggests, the figure of eight device is shaped like the number '
8', except that the section where the two 'rings' join is normally 'stretched'. One of the rings is larger in
diameter than the other. They are usually made from
aluminium, (for
strength and
weight considerations).
To use a figure of eight, the smaller ring of the device is held in one hand whilst a loop of climbing rope is held in the other. The rope loop is passed through the larger ring and then the smaller ring is 'threaded' through the loop. Finally, the slack is taken up such that the top of the loop is wrapped around the middle section of the figure of eight, (it should end up looking like you took one end of the rope, fed it through the large ring, round the 'neck' of the figure of eight and back down through the large ring again). Once the rope is is place correctly, the figure of eight is attached to the harness by clipping a karabiner through the 'small' ring of the device. Friction is controlled by varying the angle at which the rope passes through the device.
Although good for both abseiling, (descending), or belaying, the figure of eight has the advantage of the Stich plate when used for abseiling because it's larger mass and surface area help it dissipate heat more effectively.
Additionally, a figure of eight is a type of knot, which is commonly used in climbing. It's easy to tie and is one of the strongest knots you can tie in a rope.
Safety Note: This description is for illustrative purposes only and is not a substitute for correct training!