The double overhand knot is simply a logical extension of the regular overhand knot,
made with one additional pass. The result is slightly larger and more difficult to untie.
Used as a stopper knot.
Also it is sometimes used to secure items to posts.
Secure. More difficult to untie compared to overhand knot.
1. Form a loop.
2. Feed the working end of the rope through the loop like creating overhand knot.
3. Feed the rope through the loop one more time.