Square Knot Extension

A doubled green rope and a doubled blue rope are tied together using a square knot extension. The green rope goes through the bight of the blue rope, around the blue rope, and back through the bight, creating a square knot.

The square knot extension is the easiest way to extend your rope when tying a complicated harness.

It is secure enough to be used in the middle of a harness but is completely unsuitable for tying in any free-standing line. It will almost certainly fail if used to extend a vertical line.

For a slightly more complicated but technically superior technique that lies flatter, see the sheet bend extension.

If you’re using rope with knotted ends, you might like the lark’s head extension.

Step by step

The bight of a blue rope enters the frame from the left, going almost to the center of the frame. The two ends of a green rope enter from the right, going almost all the way to the blue rope.

1We’re going to extend the green rope by adding the blue rope to it.

A lark’s head has been made in the blue rope by folding the bight back and pulling some rope through the bight. The final result is a lark’s head, making a loop in the blue rope.

2Make a lark’s head in the blue rope.

The ends of the green rope pass through the loop of the lark’s head and double back on themselves.

3Pass the green rope through the lark’s head and back in the direction it came from.

The bight of the blue rope has been flipped over, so the blue rope no longer crosses over itself, instead simply forming a large, spread-out bight. The green rope goes under the edge of the loop on the right, over the edge of the loop on the left, crosses under both parts of the blue rope, over the blue rope on the left, and finally under the blue rope on the right. The green rope now makes a U shape, without crossing over itself.

4Flip the loop of the lark’s head over so that it lies on top of both parts of the green rope.

The rigger has begun to snug the knot tight. The shape is the same as before, but most of the slack is gone from the knot.

5Snug the knot into place by pulling simultaneously on the blue rope and both parts of the green rope.

The knot is fully snugged. It is tight and compact, joining the two ropes together.

6The finished knot should be small, tight, and secure.

Notes for nerds

References and naming

This knot doesn’t appear in ABOK.

This is just a clever way to make a Square Knot (ABOK 1402) tied in one doubled rope and one single rope.