What is the main function of a stopper knot?

The main function of a stopper knot is to prevent a rope from sliding through a device, which is critical in various rescue and climbing situations. Stopper knots are tied at the end of a rope to ensure that it does not slip through a belay device, pulley, or other hardware, which can lead to uncontrolled descents or loss of equipment.

When a stopper knot is used, it effectively creates a barrier that stops the rope's movement, allowing for secure control and safety during maneuvers. This is especially important in scenarios where falling or sliding could result in dangerous consequences or equipment loss.

Other functions, such as securing two ropes together or creating a loop, are performed by other types of knots designed specifically for those purposes, while providing friction during belaying is more related to the mechanics of the belay device itself rather than the function of the stopper knot.