Page 264 - Buck Tilton - Outward Bound Ropes, Knots, and Hitches 2 ed.

When something needs to be attached midrope, the loop

knot works well. This knot is important for shortening and
keeping a damaged rope functional. With the damaged part
in the middle of the knot, at the top of the bight, it is put

under no strain. Using a knot to “strengthen” a damaged
rope is an emergency measure to prevent the rope from

failing before the climb has ended. Be warned: Any
damaged climbing rope needs to be replaced as soon as

possible. And also be warned: The loop knot is not designed
to bear critical weight. For a critical weight-bearing midrope

knot, use the alpine butterfly (see page 103).

Loop Knot: Step 1