We can distill the essence of modern fly fishing to a single word: plastic. Before World War II, fly fishers used split-cane or metal rods, braided lines, and gut leaders. The best prewar gear worked very well, but it required a lot of maintenance and cost what was then a lot of money. Cheap rods, lines, and leaders persuaded many budding anglers to take up golf or some other foolishness. In the late 1940s and early 1950s, plastics technology brought us inexpensive, durable, and practically maintenance-free rods, lines, and leaders, and it brought fly fishing within the reach of millions of people. There's some strange irony in here somewhere, but let's not dwell on it.

Nylon monofilament comes in many varieties, and it remains the most popular type of fishing line. Some nylons are supple and elastic; others are much harder and stiffer. For fly fishing, we generally use mono that ranges from moderately soft to very limp and extra-stretchy, though saltwater anglers and some bass fishermen use harder nylon for leaders and tippets. By and large, good knots are easier to tie in soft, stretchy line than in hard, stiff mono.

The following comments are not a comprehensive treatment of line-to-hook knots. But my suggestions are based on experience, advice from experts, and well over a thousand knot-versus-knot tests. If a typical fly fisher combines the information in this chapter with the suggestions in the previous two, he will almost certainly have terminal tackle that is much stronger than whatever he's been fishing with.

The Clinch Knot

Bad news first: Of all the knots that I deliberately broke in freshwater tippets, the clinch consistently proved the weakest, with the occasional exception of the Duncan loop. In one small bunch of tests, clinch knots in 6X nylon failed at a paltry 81 percent of the material's baseline strength. That doesn't mean that the clinch is always an 80 percent knot — but it does show how poor it can be in light line.

On the other hand, the clinch knot is simple, consistent, and economical. And it's the responsible choice for an angler who uses a second-rate connection between the leader and tippet.

If you choose to stick with the clinch, tie it well. My tests indicate that a six-turn clinch always beats a five-turn clinch in light nylon. A seven-turn knot is better still, beating the six-turn clinch in 80 percent of my tests.

The line performs some interesting gymnastics as the knot tightens, so always lubricate a clinch before drawing it tight. Pull it up smoothly, not with a jerk, and pull only on the standing line, not on the tag end. Pull hard to seat the knot; it pays to deliberately break a few dozen clinch knots to get a feel for how hard you can pull. Don't clip the tag end flush; leave a little room for slippage.

The improved clinch knot seems to offer no improvement. In most of my knot-against-knot tests, the standard and improved versions came out about even. When there was a difference, the standard clinch beat the improved one 60 percent of the time. In this case, indoor tests confirmed my experiences in the field over many years.

Pay attention to the relative diameters of the tippet and the hook wire. If you clinch-knot 6X material to larger and larger hooks (made of thicker and thicker wire), you will reach a point at which the knot won't pull up — it simply slips until it comes undone. If you don't believe me, try clinch-knotting a very fine tippet to the biggest saltwater fly you can find.

The problem is that somewhere between a size 16 dry fly and a size 6/0 marlin streamer, there is a hook with which 6X material makes a clinch knot that seems okay but is actually much weaker than you expect. A good trout takes the fly and immediately breaks the knot.

The trick is knowing how large a heavy-wire hook you can use with a clinch-knotted tippet. I've settled on a rough guideline called the Double the X Rule. Double the X size of the tippet, and you'll have a good idea how large a wet-fly or nymph hook you can use. That is, with a 5X tippet and a seven-turn clinch knot, you're probably safe with a size 10 nymph: double 5 and you get 10. With a 6X tippet and the same knot, do not use a nymph or wet fly larger than size 12 (6 times 2). If you want to cast a size 6 streamer and insist on using a clinch knot, use at least a 3X tippet.

Although it performs poorly in light materials, the clinch knot remains useful with heavier tippets. For one thing, you can get it to tighten in virtually any tippet material. The clinch usually works well enough with 0.010-inch and heavier tippets because even a relatively inefficient knot provides enough strength-85 percent of 12-pound-test is still more strain than you can apply with any any rod short of a tarpon stick. In light tippets, though, it's a poor choice.

The Nonslip Mono Loop

Loop knots have several benefits: more freedom of movement, a slightly faster sink rate, and no worries about the relative diameters of the line and the hook wire. Loops are good; some anglers use them almost exclusively.

The two most popular loop knots for attaching flies are the Duncan loop and the nonslip mono loop described by Lefty Kreh and Mark Sosin in Practical Fishing Knots. I had long used the Duncan loop, because it seemed easier to tie. But my tests revealed that there's no contest between the two. When it's tied correctly, the nonslip loop always beats the Duncan loop. Always. In 100 percent of tests. Period. Done.

The nonslip mono loop also beat the clinch knot in 100 percent of my tests, and almost always beat the Palomar and Trilene knots, which are often touted as among the strongest connections. With any nylon that I tried, the nonslip mono loop tied according to Kreh and Sosin's instructions proved as consistently strong as any other knot; that is, no other knot beat it more than half the time. In test rigs made with two nonslip loops, the knot occasionally achieved 100 percent efficiency with the line breaking somewhere between the two knots. In light nylon, the nonslip mono loop appears to be the strength champion. It doesn't do particularly well in the economy department, though that's the least important consideration. It creates no deformation of the line.

With practice, you will make the loop smaller and use less line tying it. When I first tried this knot ten years ago, I used 6 inches of line tying the thing and ended up with a loop 2 inches in length. Now I can make nonslip mono loops less than 1/2 inch long. This knot often calls for a "third hand," as described earlier in this chapter, since tightening the wraps before seating the knot involves pulling in three directions.

Do not clip the tag end flush. Leave a little stub; 1/16 inch will do. The nonslip loop is a fairly long knot, and it stretches a little under extreme tension.

Do yourself a favor and learn this knot. If you've been using the Duncan loop (also known as the uni-knot) with freshwater tippets, stop. The nonslip mono loop is much stronger and more reliable. Instructions are at the end of the chapter.

The 16-20 Knot

I learned this knot by editing an article written by E. Richard Nightingale for American Angler magazine (the piece appeared in the March-April 2002 issue). Mr. Nightingale, the author of a book called Atlantic Salmon Chronicles, discovered the knot on his own, but I suspect that knots, like fly-tying tricks, are "invented" by many people, and this one probably has a dozen originators. In a letter written in early 2004, Lefty Kreh told me that this knot has been around since the 1950s, when he knew it as the fisherman's knot. Some folks maintain that the 16-20 is the same as the Pitzen knot, which came from Europe. The more anglers you know, the more you believe in synchronicity.

Mr. Nightingale's name for the knot, the 16-20, derives from "the 16-20 club," which consists of fly fishers who have caught 20-pound Atlantic salmon on size 16 or smaller hooks. He has performed this unusual feat.

Actually, Mr. Nightingale calls it the 16-20 loop knot, because it begins as a sliding loop and finishes by tightening around the standing line. That's a nice distinction, but it creates the wrong impression. The 16-20 knot does not form an open, free-swinging joint. Although it tightens around the standing line, it does so against the hook eye. So, I have shortened the name to 16-20, deleting the suggestion of a loop.

The 16-20 has one drawback that doesn't matter in most trout fishing: It doesn't work with heavy line. With 3X and lighter nylon, it's easy to seat properly. Getting a 16-20 knot to seat in 2X and heavier tippets is harder and often impossible. This is a knot for 3X and lighter nylon; you simply can't tie it in heavy stuff.

So why learn it? Because it's a superb knot. In the 3X through 6X nylon materials with which I compared knots, only the nonslip mono loop and Orvis knot proved consistently stronger; the 16-20 trounced every other knot. The 16-20 bested the Trilene knot about 90 percent of the time. It beat the clinch knot every single time, and almost always beat the Palomar knot. Like the nonslip loop, it sometimes achieves 100 percent efficiency.

The 16-20 forms a remarkably small knot. With dry flies, emergers, and small nymphs, that's a good thing. The 16-20 also creates little or no deformation in the line.

Although the 16-20 is a simple knot, it's awkward to learn. The motions and hand positions are not like those involved in making most other knots. I find the 16-20 easiest to form if I start by pulling about 6 inches of line through the hook eye so that I can tie the knot well above the hook, letting the fly dangle below my left hand. The knot slides down to the hook before it tightens.

Tightening the 16-20 is a three-stage process. After forming the knot, pull gently on the tag end to compact the wraps. Don't pull too hard, because the next stage is to slide the knot down to the hook eye. Give the tag end another gentle tug to make sure that the wraps are compact (but still not too tight), and then pull hard on the standing line. And I mean hard, because something interesting happens when you pull with enough force. You will feel, and perhaps hear, a click as the knot seats. There's no mistaking the click — you will feel a jolt in the line. When you feel and hear that pop, the knot is seated and finished. You will also notice that the tag end comes out of the front of the knot nearly parallel with the standing line. That's your other indicator that the knot has seated properly. Since you need to pull hard to seat the knot, hook the fly on something solid such as a finger loop on your forceps.

You must feel the click and see the tag end exit the front of the knot almost parallel with the standing line. If either of those does not happen, cut the knot and tie another. More often than not, however, an incorrectly formed 16-20 snaps as you try to seat it. In effect, it has a built-in indicator of strength. Once learned, the 16-20 is childishly simple.

The diameter of the hook wire seems to have little effect on the 16-20's strength. For dry-fly and emerger fishing, where you want a small, tidy connection, the 16-20 knot is remarkably strong and reliable. You'll find instructions after those for the nonslip loop at the end of the chapter. Just remember to use it with 3X and lighter tippets, and remember the click.

The Orvis Knot

Some years ago, the Orvis Company held a contest in which anglers submitted new line-to-hook knots. A gentleman named Larry Becker won, and the knot he submitted is among the strongest, simplest, and most reliable that a fly fisher can use. The Orvis knot is also very small and light.

In 3X and lighter nylon, the Orvis knot always beats the clinch and virtually always beats the Trilene and Palomar knots. I thought that the 16-20 knot was the strongest tight-to-the eye connection in light nylon until I tested it against the Orvis knot. In fifty tests made with 3X through 6X materials, the 16-20 broke twenty-six times and the Orvis knot broke eleven times. In the remaining thirteen cases, neither knot broke; the line parted somewhere between them.

Unlike the 16-20, the Orvis knot works well in heavier lines. It's easy to tie in the fairly stiff, 0.011-inch spinning line that I sometimes use for saltwater and heavy bass-fishing tippets. It's also absurdly simple and almost impossible to screw up.

The Orvis knot does have one drawback: It wants to cock at an angle as it's tightened. If you begin the knot with the hook upright, the line cocks at an upward angle; if you start with the hook upside down, the line ends up cocked downward. You can easily push or pull the finished knot into correct alignment, but it might cock again while you false-cast. How much this matters depends on the fly and the situation. With a bushy dry fly, a cocked knot might result in a twisted tippet. The problem probably will not occur with a size 6 stonefly nymph.

The Orvis knot's great strength and simplicity make it worth using for some, if not most, of your fishing. It seems to work well in virtually any tippet material. Instructions are after those for the 16-20 knot.

The Trilene Knot

Since I'd long used this popular knot and always regarded it as strong and secure, I included it my comparisons. For the most part, it justifed my faith. The nonslip mono loop, Orvis knot, and 16-20 consistently beat the Trilene knot in 3X and lighter materials, but the Trilene beat the other knots I tried. In light nylon, it is always stronger than the clinch (winning 100 percent of contests) and usually stronger than the Palomar.

The Trilene knot requires you to pass the tippet through the hook eye twice. That's a problem with a small fly, but also irrelevant, since other knots work better with fine tippets. With a bigger hook, you'll have no trouble poking the tippet through the eye twice. And by a happy coincidence, the Trilene knot seems particularly efficient in heavier materials that you'd use with large flies. In the 0.010- through 0.012-inch nylon lines that I've tried, the Trilene knot beats the Orvis knot more than half the time, always beats the clinch knot, and comes out about even with the nonslip mono loop. I can't explain this; I merely report what I've observed. For attaching a big bass or saltwater fly to a stout tippet, the Trilene knot is an excellent choice.

Tie it with five turns, wet it before drawing it tight (this reduces the knot's tendency to deform an inch or so of line), seat it firmly, and leave at least a 1/16-inch tag end. You can find instructions in any number of books and on many websites.

A Small Group of Nylon Knots

If you use a good connection between the leader and tippet, you can safely use several high-strength knots for attaching flies. To make a free-swinging junction, use the nonslip mono loop. If you want a tight-to-the-eye knot with a 3X or lighter nylon tippet, attach the fly with a 16-20 knot or an Orvis knot. Any of these three knots might even let you drop down a size in tippet diameter, and that translates into more strikes. With a heavy tippet, use the Trilene knot to make a tight-to-the-eye connection.

If you decide to stick with a second-rate tippet knot, then attach your flies with a plain old clinch or a Duncan loop. You will avoid breaking off entire tippets and littering the waterways. But be aware that with some materials, you might have a rig that retains as little as 70 percent of the line's actual breaking strength. I'm not making this stuff up. In one batch of tests made with a digital scale, I watched five consecutive blood knots in 6X nylon fail at an average of 65 percent of the line's baseline strength. Stick with your old knots if you want, but know that you will lose more fish by doing so.