The Fliskits Tres 24 comes with one of those really fat shock cords to attach to the nosecone and parachute, and skinny kevlar shock cord that attaches to the engine mount. What is the best way to tie these very different cords together? See photos.
The Sheet Bend or Weaver's Knot is recommended for joining two ropes of unequal size. The thicker rope must be used for the simple bight as shown. However, it works equally well if the ropes are of the same size.