Stopper knots create a well-defined area of thickness in an otherwise uniform rope to prevent it from slipping through a narrow passage. They range from the simple overhand knot to the elaborate monkey’s fist. The complex knots belonging to this category are big and frequently used for decorative purposes. Other uses include sailing, climbing (belaying) and fishing. They are usually tied at rope ends to prevent them from slipping through another knot, retracing through a block, hole, belay or rappel device.