The prusik knot or prusik hitch is a friction hitch knot most commonly used by climbers for ascending. It is named after Karl Prusik, an Austrian mountaineer who introduced this knot in 1931.
Rescue teams such as Swiftwater rescue use a Prusik knot as a 'pulley tender' hitch, to hold a line taut while tensioning a highline for a Tyrolean traverse, or in boat-on-tether and similar rescue operations.
The Prusik knot offers a way to ascend on a climbing rope using slings, smaller diameter rope, or cord. The knot slides freely along the rope but will grip firmly when weighted. In its simplest form, it is a girth hitch tied twice:
Alternatives uses for the prusik knot:
This knot can slip on worn ropes, and for the purpose of ascending its use is largely superceded by mechanical ascenders. Aside from emergency situations, its most common use in mountaineering and climbing is now as a backup knot. In this application, it is often known as a dead-man's hand for abseiling. Should the abseiler release their brake hand, the knot prevents them falling out of control when it is tied around the fixed rope, below the descender, and attached to the harness.
It can also be used to hold cylindrical objects.
Similar, alternative knots include the Klemheist, Bachman and Autoblock knots. The Klemheist tends to be easier to slide up, but does not work well with webbing. The Bachman is less liable to slip when tied with webbing, but requires a carabiner.