A tapered flats leader is comprised of a butt section, midsection and tippet. But rarely will you use only three strands of monofilament to build one due to its length and the diameter disparity between the sections. In fact the best midsections for transferring casting energy from your fly line to your light tippet have anywhere from two to four sections, depending on the overall leader length (longer leaders require more strands in the midsection).
If you will take the time to build a multi-strand leader midsection, the payoff is better turnover and accuracy, particularly in the wind. Plus, your knots will be easier to seat, and will be stronger because you’re joining strands that are similar in diameter, rather than tying a heavy butt to light tippet directly. And speaking of diameter, in the following diagrams, pound-test references are used, and the specific diameters are as follows, with perhaps small variances between brands of line: 40-pound test (.026); 30-pound test (.023); 20-pound test (.019); 15-pound test (.016).
Tie sections together with blood knots, back-to-back uni-knots (a.k.a. Duncan loops) or surgeons knots, Since you are tying together slightly differing diameter lines, you might find that one less wrap (if using blood knot or uni-knot) of the heavier material will help you draw the knot down better, and not sacrifice breaking strength. Lubricate your knots with water or saliva before seating to prevent friction (heat) damage.
Since you’ll be storing these long leaders in coils, which causes memory, before fishing, always take a moment to straighten them by stretching them out a bit. A leader with coils will not turn over well, plus will dampen the action of your fly on short strips. Attach butt section to fly line via a nail knot, needle nail knot, or by tying a perfection loop or surgeons loop in the end of the butt section (as depicted in diagrams), and then loop it to a whipped loop in the end of your fly line.
The following diagrams are of typical tapered leaders that work well for sight casting. These can be tweaked to your specifications.
Ten-foot leader using the 50-30-20 formula (good for delicate presentation).
Ten-foot leader using the 60-20-20 formula (better for windy days).
Twelve-foot leader using the 50-30-20 formula (excellent for delicate presentation).
Fourteen-foot leader using the 50-30-20 formula (excellent for delicate presentation).
