The easy-to-cast constrictor knot is frequently used as a secure binding for closing a sack or to fasten a line to another line for in-line pulling (D.).
Difficult to untie, the constrictor knot should be used where you desire a permanent knot. In practice, the ends are frequently heat-melted so the knot cannot be untied.
A. To apply the knot, take a turn around the objects to be tied, pass the bitter end over the working part, and take another turn around the objects to the left of the working part. As the arrow shows, bring the bitter end over the working part and up under the bottom and top parts of the first turn.
B. Pull tightly on the bitter end and working part to cinch the knot.
C. & D. To provide for a parallel pull on the working part, add a half hitch with the bitter end as shown. To improve pulling ability still more, add as many consecutive half hitches as required to prevent slipping.
Original materials used with thanks to Irene Rodriguez and John Bennett