Article: The double overhand knot is simply a thicker stopper knot and is used to keep the rope from passing through large openings or holes. It can also, however, help you create several other knots:   Double Fisherman's Knot: Takes two separate ropes and ties them together with two double overhand knots.   Double Overhand Noose: A more complex knot that uses the same basic theory as the double overhand, put provides an adjustable snare at the ropes end. The double overhand knot is a large stopper, but you may want even more size. To do so, simply keep moving the rope through the loop as many times as you want to make a triple, quadruple, or even bigger knot. These are simply called "multiple overhand loops."

What is a summary?
Use the double overhand knot for larger stoppers, or as part of other, more complex knots. Loop the end of the rope as many times as you want to increase the size of the stopper.