Double fisherman's bend

The two ends lie side by side, pointing in opposite directions. Each end is wrapped twice around both strands and then tucked back through those two wraps – that is a double overhand knot lying around the other rope. Each of these knots can slide along the other rope on its own, like a bead on a string.

When the standing parts are pulled, the two knots slide towards each other until they meet. From then on they block each other: neither can slide further because the other is in the way. Under load the wraps cinch down very tightly. That makes the knot secure – and at the same time so hard to untie.

The double fisherman's has an easily recognisable pattern. On one side you see two “X” shapes, two crossings side by side. Turn the knot over, and on the other side four parallel strands lie next to each other. If the two halves nest together this neatly, they are correctly mirrored. If one side looks different from what you expect, usually one of the knots has been tied the wrong way round.

To set it, first pull each half tight on its own, then pull on both standing parts until the knots meet. The tails must then stick out clearly – rather too long than too short, because under load some tail is drawn into the knot. A tail that only just peeks out is a warning sign.

A common mistake is tying single instead of double overhands. That gives the single fisherman's knot, which is fine for light uses but less secure. A second mistake: the two knots are not mirrored, so they do not nest neatly. And third: tails that are too short.

For beginners, mistakes in this knot are hard to spot, because it can look compact even when tied wrongly. That is why the pattern of two X shapes and four parallel strands matters so much – it is the quickest check. It is not meant for flat webbing; the water knot is used for that.

It is the right choice for permanent joins: two cords that will not be separated again, or accessory cord closed into a loop, for example for a prusik. It also holds well in slick cord in which a sheet bend would slip.

If you want to undo the join soon, choose another knot, such as a sheet bend or, for thick ropes, the carrick bend. It also uses a lot of rope. In mountaineering it is taught on courses, and this page does not replace that training. Life-safety use only after proper training with certified equipment.

First practise the double overhand on its own until you can tie it confidently. Then take two cords of different colours. That way you can see exactly where each strand runs, and it is much easier to recognise the pattern of two X shapes and four parallel strands.

Tie the knot several times, set it, turn it over and check both sides. If you deliberately tie it once with halves that are not mirrored, you will see how different it looks. This knowledge helps you spot mistakes immediately later on.