The reef knot or square knot is an ancient and simple binding knot used to secure a rope or line around an object.
The square knot is used to tie the two ends of a single line together such that they will secure something, for example a bundle of objects, that is unlikely to move much. The knot lies flat when made with cloth and has been used for tying bandages for millennia. As a binding knot it was known to the ancient Greeks as the Hercules knot (Herakleotikon hamma) and is still used extensively in medicine. It has also been used since ancient times to tie belts and sashes. A modern use in this manner includes tying the obi (or belt) of a martial arts keikogi. With both ends tucked (slipped) it becomes a good way to tie shoelaces, whilst the non-slipped version is useful for shoelaces that are excessively short. It is appropriate for tying plastic garbage or trash bags, as the knot forms a handle when tied in two twisted edges of the bag.
The reef knot’s familiarity, ease of tying, and visually appealing symmetry conceal its weakness. The International Guild of Knot Tyers warns that this knot should never be used to bend two ropes together. A proper bend knot, for instance a sheet bend or double fisherman’s knot, should be used instead. Knotting authority Clifford Ashley claimed that misused reef knots have caused more deaths and injuries than all other knots combined. Further, it is easily confused with the granny knot, which is a very poor knot.
Reef knot, Square knot, Hercules knot.
A reef knot is formed by tying a left-handed overhand knot and then a right-handed overhand knot, or vice versa.