The
reef knot, or
square knot, is an ancient and simple
binding knot used to secure a rope or line around an object. It is sometimes also referred to as a
Hercules knot. The
knot is formed by tying a left-handed
overhand knot and then a right-handed overhand knot, or vice versa. A common
mnemonic for this procedure is "right over left; left over right", which is often appended with the rhyming suffix "... makes a knot both tidy and tight". Two consecutive overhands of the same
handedness will make a
granny knot. The
working ends of the reef knot must emerge both at the top or both at the bottom, otherwise a
thief knot results.