Figure Eight Follow Through

 
This knot is used to tie ropes of equal diameters together or to tie a rope around an object, the end of which is not available.
   

Step 1 - Tie a figure-eight knot on one end of the rope.

   

Step 2 - Feed the end of the other rope through the figure-eight knot in reverse. It should follow (hence the name) the exact path of the original knot.

   

Step 3 - Use a safety knot, such as the overhand, with this knot

Note: The figure-eight follow through can be tied in the middle of the rope by placing the gifure eight at a point far enough along the rope to allow sufficiient rope to go around the object.