Figure eight

Figure eight
Other names	Figure 8, eight
Use(s)	Tying onto the rope end/middle, end-knot (single strand, marking)
Pros	Reliable, easy to inspect, low decrease of the rope strength
Cons	Tedious to untie after a lead fall in some cases, figure-eight bend is prone to rolling
Category	Knot
Strength	~60-80% in normal (non-ring) load. Differs by author, type of measurement and rope

The Figure-eight loop is the most common way how to tie onto the rope. Together with a re-threaded bowline, it is one of the two widely accepted knots for tying-in at the rope end. It is popular for its reliability and visual clarity, which makes it easy to inspect. It can be difficult to untie after bigger lead falls, especially if it was not properly pre-tightened. Closely related figure-8 bend knot is prone to roll.

Tying

Follow-through (tie-in on the rope end)

This method is the most commonly used method for tying-in onto a rope end.

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  Take a bight of a rope and turn its one end around the other, making a full 360° turn (1)

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  Pull the rope through the upper eye (2), creating a figure-eight knot

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  Pull the rope through both eyes of a harness next to the belay loop (3)

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  Continue by following-through... (4)

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  ... the original figure-eight (5)...

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  ... knot (6)

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  Tighten the rope ends one at a time (7,8,9,10)

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  Inspect the knot and check if the loop is threaded through the harness correctly (11)

The inspection described in the last step should be also done as a part of a partner check.

On a bight (tie in in a middle)

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  Take a bight of a rope and do a bend (1)

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  Make a full 360° turn of the bend around the rope strands (2)

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  Pull the bight through the loop made by the turn (3)

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  Slightly tighten the knot (4)

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  If the knot is malformed, dress it for easier inspection (5)

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  Inspect the knot (6)

Preventing from getting stuck

In some cases, Figure 8 tends to get hard to untie. To prevent this issues, always dress the knot and tie its form where the load strand goes in a bigger diameter around the center of the knot, as illustrated below. This variant also has a slightly higher loading limit according to some sources (10% difference, both variants are completely safe). The issue of figure 8 getting stuck was well studied and documented/illustrated by Hard is Easy. If the figure 8 is not dressed and tightened properly before loading it, it tends to malform substantially after taking a fall. Malformation leads to a knot state in which the figure 8 is hard and sometimes even almost impossible to untie. Rope parameters (diameter, stiffness) also play a role. Last very important parameter discovered was if the load strand goes on the top of the knot, or in the middle of it.

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  By properly pre-tightening the knot before loading, you minimize the chance of getting it stuck

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  Allegedly slightly stronger variant. It is easier to untie after a fall

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  This variant is more prone to get stuck after big lead falls

Rolling

When the ropes coming from the figure 8 are pulled in the opposite directions, the knot might capsize and roll over itself

The Figure 8 bend knot can capsize and roll over itself already around 3 kN of force (then it snaps). For that reason it is not an ideal knot for tying two ropes together. There are speculations that the usage of Figure 8 bend knot during rapelling is the reason why the overhand-bend knot is known as an European Death knot in US.