Constrictor knot

The constrictor is a clove hitch with an extra trick. On the final tuck, the end is passed not only under the diagonal turn but straight after that under the standing part as well. This makes the two ends form an overhand knot under the crossing – the simplest knot of all, the first step you know from tying shoelaces.

The diagonal turn lies across this overhand like a clamp and presses it onto the object. When you pull the ends, the overhand gets tighter and the diagonal turn holds it in place. Because the forces reinforce each other, the knot does not loosen by itself. It works best on round objects, because the pressure there is even all the way round.

From above, a finished constrictor looks like a clove hitch: two parallel turns and a diagonal turn crossing over them. The difference is hidden underneath. If you lift the diagonal turn slightly, you should see the two ends wrapping around each other in an overhand knot under it. If the ends just come out in parallel under one turn, you have tied a clove hitch.

It is set hard: pull both ends at the same time until it bites deep into the object or the wrapped cord. With thin cord it helps to wrap the ends around a stick so you can pull harder. If it is to stay permanently, trim the ends short; if it needs to come undone later, leave them longer or tie it slipped.

The most common mistake: the end is tucked only under the second turn. Then it is not a constrictor but a clove hitch, which works loose much more easily when things move. A second mistake is using it on flat or square objects and relying on its grip. Over corners the cord does not lie snug all round, and the pressure is uneven.

It can also fail if the cord is too thick and stiff to bed down tightly, or if it is very slick. The double version with an extra turn helps then. Good to know: a constrictor is not a substitute for a hose clamp on a pressurised line, and it is not a knot for carrying loads.

Wherever something round should stay firmly bound for good, the constrictor shines: the neck of a sack, a bundle of poles or brushwood, a rope end before cutting so it does not unravel. In DIY it can serve, for example, as a temporary clamp while gluing.

It is unsuitable for anything you will want to open soon, because often only a knife helps then. A clove hitch or the slipped version is better there. And once more, explicitly: never tie it around body parts. It closes so tightly that it can cut off blood flow. First aid has its own rules, which you learn on a course.

When the knot has to go, place the knife on the diagonal turn that lies over the crossing. Once that is cut, the remaining turns usually fall away by themselves. This way you avoid cutting into the object beneath – such as a rope, a sack or a piece of wood you still need.

Always move the blade away from your body and your other hand, and hold the object so that a slip will not hit you. With very tight knots, a small sharp blade is safer than a lot of force with a blunt one. Children should do this only under supervision.