An autoblock knot is easy to tie friction knot that is tied around a climbing rope with a thin length of cord. It slides freely over the rope during a controlled descent, but jams in the event of a sudden drop thus stopping the descent.
The autoblock is very similar to the Klemheist knot, the only difference is that in the last step the both tails are simply clipped together with a carabiner instead of feeding one through the other.
Used as a safety backup knot when rappelling. The knot is tied below the rappel device and it slides down the rope as the climber rappels down.
Non-jamming and gripping. Unlike other friction knots, it releases while still under load.
– Check that the sling is not too long or it will jam in the rappel device when it’s weighted.
– Make sure that the knots on the autoblock cord are not touching the main rope.
– If there are not enough wraps the autoblock will slip. If too many wraps are used, the knot won’t slide easily.
– Since the autoblock cord is under friction regularly check it for wear and tear.
Autoblock knot, French Prusik knot