Vertical caving terminology and methods > Personal SRT gear
A piece of strong cord, tied in a friction hitch such as the Prusik knot, that slides up the rope when pushed up, but remains static when one end is pulled. Used as an ascender if you hate yourself. Using a prusik loop or prusik tether for prusiking is painfully slow and laborious compared with dedicated ascenders, and makes manoeuvres such as rebelays slow and awkward. There is also the risk of dropping it, since it normally needs to be completely removed from all other equipment when it is being connected or disconnected from the rope (and keeper cords cannot be used). Favoured by climbers, or as an emergency backup, because of its low weight. The cord should be 3 mm smaller in diameter than the rope it is being used with. The cord is normally tied into a loop using a double fisherman's knot, but for some friction hitches, it is used as a tether normally tied with poacher's knots at the ends. This may be known by climbers and arborists, particularly in the USA, as just a "prusik", but this confuses it with everything else that uses that name, such as Prusik knot, other friction hitches and prusiking. As a result, it is best to use a more specific term. The name "sling" is not used often any more, which is good, because it confuses it with a sling. American cavers who used prusik loops would often talk about using "knots" or climbing a pit using "knots", but this rather unhelpfully confuses it with all the other knots that get used for SRT. The minimum breaking strength of a prusik loop or prusik tether is quite complex. The cord must be strong enough to support a person, after all of the knots have been tied. A prusik loop is doubled (a prusik tether may or may not be, depending on which knots are used), so its strength is doubled, but the knots then reduce it by about half, so the resulting strength of the cord is about the same as its minimum breaking strength. However, it will not be able to grip the rope with that strength. A prusik loop or prusik tether is expected to slip down the rope when subjected to extremely high loads, which helps to absorb any shock loads if a caver somehow falls onto one (such as by holding it incorrectly, causing it to stop gripping the rope until it is released). The exact load at which it slips will depend on the diameters of the rope and cord, and the specific friction hitch that is used. The working load limit will, by necessity, be lower than that.
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