Ascenders are mechanical devices for ascending on a rope. They are also called Jumars, after a popular brand.
Jumars perform the same functionality as friction knots but are stronger, faster, safer and less effort is needed to use them. A Jumar employs a cam which allows the device to slide freely in one direction but tightly grip the rope when pulled on in the opposite direction. To prevent a jumar from accidentally coming off the rope, a locking carabiner is used. The Jumar is first attached to the climber's harness by a piece of webbing or sling, and then the Jumar is clipped onto the rope and locked. Two ascenders are normally used to climb a fixed rope. For climbing a fixed rope attached to snow anchors on a steep slope, only one Jumar is used as the other hand is used for holding the ice axe.
Another type of ascender allows rope to feed in either direction, slowly, but locks up when pulled quickly. Such self-locking devices allow people to protect solo climbs because the amount of rope is automatically adjusted.
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