A heddle is a set of looped strings with a center eye which the warp thread passes through to make a path for a weaving shuttle. Heddles can be rigid or made of string depending on the loom and weaver's preferences. There is a heddle for every warp thread. So a kitchen towel may have 3 to 400 heddles and larger, and finer woven items will have more. This is one reason to make your own heddles, as you will need a lot of them.
Measure from the top of the upper heddle carrying bar to the bottom of the lower heddle carrying bar. This is the length of your heddles. Cut heddle cord twice the length plus 6 inches. Set up a jig (two posts the right distance apart) to make cutting your cords faster. You will often need more than 1,000 at a time.
Place a cutting mat along the edge of a table so you can read the measurements on the mat.
Position a squeeze clamp so that the bar of the clamp is upward. Locate one clamp so that the outside of the upright bar is at your upper heddle measurement and the other clamp's outside bar is at 0. Double check your measurements. The measurement to the outside of each bar should be your heddle measurement.
Position two of the same type of clamps in the center. The wide part of the clamps will touch at the exact center mark. Check your measurements.
Fold a heddle cord in half. Place the folded loop end over the left upright bar. Tie a square knot. Bring the right cord over the left and pull the ends to bring the knot up against the bar. Bring the left cord over the right to complete the knot and pull the ends tight. Take your cord ends past the next bar. Make the same knot on the right side of the second bar. Take your cord ends past the third bar. Make the same knot on the right side of the third bar. Take your cord ends past the fourth bar. Make the same knot on the right side of the fourth bar. That is one heddle. Repeat for as many heddles as you need.
Tie your finished heddles together in bundles of 10 so make them easier to count and to keep them untangled until you install them.