The Prusik knot was first used in the early 19th century by Dr. Karl Prusik (a physician). Because it is so versatile, the term "prusik" is generally used to refer to this particular knot. First, take a kernmantle rope that is 5–6 mm in diameter and 35–40 cm long, and use a double fisherman's knot to join the two ends into a loop. Place the loop behind a main rope that is 9–11 mm in diameter.
Uses of the Prusik knot:
1. For ascending a main rope, functioning similarly to an ascender;
2. Used as a safety backup when rappelling;
3. Serves as one of the key components in constructing a rescue pulley system.
Notes:
1. The diameter of the kernmantle rope used for the loop must be smaller than that of the main rope. The loop rope should be at least 5 mm in diameter, and the main rope should not be less than 9 mm. To be safe, the loop rope is usually 6 mm in diameter, while the main rope is 9.8–14 mm in diameter;
2. Wrap the rope around the main rope 3 times;
3. If using a thicker kernmantle rope, such as 7 mm, fewer wraps (usually 2) are needed, but the performance is not as good as using a 6 mm rope.