stopp1This is a Stopper Hitch. It is a knot that applies pressure. Pressure that increases with the weight you apply to it. Used most often in two situations: 1. attaching sand bags to ropes and 2. tying a counter weight line to the locking rail to indicate that the line is to stay put.

The smaller line gets one wrap around the big line.  stopp2
Then it passes over itself.  stopp3
Under the big line again.  stopp4
Then in between itself and the big line several times. 4 is a good number. I hope the riggers out there will let us know if there is a standard number of wraps.  stopp5
I used 4 wraps. Notice how the small line keeps wrapping inside itself.  stopp6
Pull it tight.  stopp7
The small line is tied to the locking rail below.  stopper8
This knot will allow itself to be adjusted simply by relieving the pressure. Without the pressure, the knot slides up and down with ease.  stopp9