Autoblock
An autoblock (or autobloc or "third hand") is a rope device used in climbing and caving for both rappelling (downward) and ascending (upward).[1][2]
While rappelling, it slides freely down the rope when pushed downward by the hand, allowing a controlled descent, but jams in the event of a sudden drop or loss of control, stopping the descent. This prevents uncontrolled falls in the event of an accident in which the rappeler loses control of the rope.[3] For ascending, it likewise can be pushed up the rope manually when unweighted, but jams and holds when weighted by the body.
It is made using a friction hitch around the rope, connected by a carabiner to the climber's harness, and may be combined with other climbing equipment for further safety.[4] For instance, it is typically used as a backup while rappelling using a tube belay device.[1]
The term autoblock is also used for a specific type of friction hitch,[5][2][6] which is also known as a French prusik or Machard knot, named after its inventor, Serge Machard.[7][8]
Other friction hitches that can be used to build an autoblock system include the Prusik knot, Klemheist knot, and Bachmann knot.
The Ashley Book of Knots #505.
See also
References
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