A large paper clip is used. It has just the right amount of tension.
Tie your string at the large blue line after bending the clip as shown. You can use bare string or pull the string over jewelers rouge or polish before tying it to the tool. The type of string used affects the performance of the tool. The string can be moved up a notch on the right to get a better angle to work at.

that is pretty cool Patrick.
will try it when i am able.
Todd