The Double Alpine Butterfly Loop, also known as lineman's loop, butterfly knot, alpine butterfly knot and lineman's rider, is a knot used to form a fixed loop in the middle of a rope.
The Double Alpine Butterfly knot is essential for climbing and not too difficult to learn how to fasten. The Double Alpine Butterfly knot provides great support for a carabiner.
The Double Alpine Butterfly knot can be used to double loop and object or allow multiple objects to be fastened. The Double Alpine Butterfly knot is a versatile knot but not needed in most application in climbing.
The Double Alpine Butterfly knot is a great knot to learn if you are in need of double knots. The Double Alpine Butterfly knot is extremely safe and does not degrade the rope that much.
Usage: The loop is typically attached to a climbing harness by carabiner.
It can also be used to isolate a worn section of rope, where the knot is tied such that the worn section is isolated in the loop (which of course does not receive a carabiner nor bear any loads in this case). The loop portion is isolated when the other two legs are loaded, and in fact the butterfly can be tied as a bend with the ends emerging where the loop would be.
Errors in tying the butterfly loop can produce a similar looking but inferior knot, the so-called "false butterfly", which is prone to slipping. However, some sources suggest this behavior can be exploited purposely for shock absorption.