fisherman's knot. A sling or Prusik-dedicated sewn loop can also be used. Note that Dyneema/Spectra has a very low melting point and should not be used in Prusik hitches unless the cord or sling is specifically engineered for it (as seen in some sheathed constructions). The length of this loop depends on the application. For instance, the loop used for an Auto-Bloc might only be 20 cm, whereas the foot loop for climbing a rope might work better with a length of 100 cm or more. As a general rule, longer loops are preferable over shorter ones, as a loop can always be shortened by tying a knot in it. The effectiveness of the Prusik hitch relies on the surface area between the hitch and the main line, and the diameter of the cord used. Normally, the greater the difference between the diameter of the cord used for the hitch and the main line, the greater the ability for the hitch to hold. However, the smaller the diameter of the cord used, the lower its safe working load. In addition, smaller diameter cords often jam too tight when placed under load, and are hard to handle when wearing gloves. Tying The Prusik is tied by wrapping the "tail" of the Prusik loop around the rope a number of times, usually 2-4 times depending on the materials, (each time, through the other (bow) end), forming a barrel around the rope with a tail hanging out from the middle. When the tail is weighted, the turns tighten and make a slight bend in the rope. When weight is removed, the loop can be moved along the rope by placing a hand directly on the barrel or pushing it from "behind". Breaking the Prusik free from the rope after it has been weighted can be difficult, and is most easily done by pushing the bow, (the loop of cord which runs along the barrel, from the top wrap to the bottom wrap), along the tail a little. This unwinds the barrel wraps to loosen the grip of the hitch, and makes movement easier. Note: Step 2 is also called a girth hitch (a single wrap) and is not a good Prusik (yet). Note: Step 4 has a twist in the webbing that is inconsistent with the preceding images, but will not affect use except to make it slightly more difficult to loosen after