Even if you use “knotless” systems to attach your leader to you fly line, you will still need to know the nail knot to attach your fly line to the backing. It’s a good idea to have this knot in your arsenal for the day your braided loop fails.
Step 1. The backing shown on top with a large loose loop in it. A two inch section of drinking straw is in the middle. The end of the fly-line to be attached to the backing is on the bottom.
With your left hand grasp the straw holding fly line along side of it from the left and the backing along it from the right. Make sure you have at least eight inches of backing left over after running it along side of the straw. Starting from the left side of the straw, wrap the end of the backing, back over itself with five loops.
After making the five loops around the straw, take the extra backing and run it through the right end of the straw as shown. Now for the tricky part, grasp all of the loops between the thumb and index finger of the right hand. While holding all the loops together, slide the straw out to the left. Pull both ends of the backing at the same time from the left and the right to tighten its grip around the fly line. As you tighten, watch the loops to make sure they stay nice and neat around the fly line.
If everything goes ok, you should have something that looks like the picture above. Now the easy part, trim the excess fly line and the excess backing. Your done! Time to go fishing.