Nylon and polyester threads are thinner and stronger than silk and therefore more practical for today's fly tying. Polyester has less stretch than nylon, which should give you more thread control. The stretch in nylon, on the other hand, gives you a buffer against breakage, and provides a "rubber-band" effect to grip materials better. Nylon thread is dyed after production and tends to have more vibrant, fluorescent colors than polyester.

Flat thread (pink) ties with less bulk and leaves a smooth finish. Twisted or round bonded thread "grabs" material better, and can be used for a rib, or for segmented bodies.

Kevlar and gel spun polyethylene (GSP) are newer thread materials. These fibers have incredible tensile strength but don't handle as well for general use, and are more expensive than polyester or nylon. Their best applications are for situations where strength is critical, such as flaring hair, wool, or egg yarn.

If well suited to the type of thread you use, bobbins can make you a more effective fly tier. Above are shown a Griffin Supreme ceramic bobbin (green thread), a Griffin Multi-thread bobbin (red thread), a Gudebrod disposable bobbin (lavender thread), a Merco ceramic bobbin (red thread), and a Griffin Adjustable bobbin. Bobbins Because thread spools are different widths and threads are different strengths, you need to adjust your bobbins to get the most out of your thread. A correctly adjusted bobbin should feed thread with enough resistance for thread tension but not such much that the thread breaks. Clip bobbins are the most common. They can be adjusted by bending the arms in or out until you have the correct amount of pressure. Thread spools can also be "palmed" with your fingertips for more pressure. There are also adjustable tension bobbins, which can be fine-tuned for your thread. I recommend ceramic tip or tube bobbins since thread won't groove them, and the thread seems to feed out of them with less friction. Thread Construction Thread comes in several different configurations. Experiment with different types to determine what is best for you tying needs. Thread Color The thread colors you choose can make your flies more attractive, and if applied properly, more effective. Nylon thread tends to have more vibrant, fluorescent colors than polyester.

Kevlar has been around since the '70s. It is generally sold in what is considered to be a 3/0 size. It has "wiry" feel to it, which I have never been fond of, but it is strong.

GSP is a relatively new product. This is the same material as the bass fishing Spider Wire and the new super thin fly line backings. It is slightly stronger than Kevlar, and has a softer feel and texture for tying. It is very slick and a drop of super glue on the hook shank before tying is a good idea.

Tying thread is sold in several different configurations. Most tying thread has a floss-like construction of multiple parallel fibers, creating a flat thread that can come with varying amounts of twist. Thread that can be flattened (untwisted before you wrap) makes it easier to produce a smooth head on the fly. Flat thread also tends to lie flatter on the hook and cause less bulk on the hook shank. Flat thread is also less prone to cut materials such as foam. Round thread, like rod-building or sewing thread, is built like rope, with a number of threads or plys twisted together.

Heavy twisted-ply thread holds material by biting into it and is a good choice if you need to spin deer hair, or build up mass with your thread, as in some saltwater flies.

Bonded thread is made semi-round by bonding parallel filaments together. It comes off the spool round, but if you warm it up in your hands, or slide it through your fingers prior to starting the fly, it will "break down" and lie flat on the hook. Bonded and twisted ply threads are more abrasion-resistant than flat thread. This can be a benefit, especially when tying bead head flies since the beads sometimes have rough edges. Also, round thread makes nice segmented bodies and can be used to rib the bodies of flies.

Removing or adding twist to any thread can change thread structure. This is accomplished by spinning the bobbin. When twisted, the thread has a little more bite and is less prone to fray. When flattened, there is less build up and a smoother finish, but it is more prone to fray.

Tying thread comes waxed or unwaxed. I prefer waxed thread because it gives me a better hold on the material, makes it easier to dub, lubricates the thread, and helps prevent fraying. The wax also bonds to itself, which keeps thread layers from slipping.

The disadvantages of waxed thread are that the wax can clog bobbins and add bulk to thread. Most waxed threads use a paraffin wax, but Uni-Products uses a rosin wax. Uni is a good compromise as you lose some lubrication, but it doesn't seem to clog bobbins.

Some water-based cements will not penetrate wax thread properly. You can use beeswax, paraffin, or dubbing wax to prepare your own thread if you need it. I am not a big fan of dubbing wax for this purpose or dubbing, as it tends to be too sticky.

Nylon monofilament (tippet material) is an attractive material because it is strong and transparent, but it stretches and relaxes after application, creating flies that fall apart unless you cover the thread with epoxy. Clear monofilament thread is different than tippet mono. It isn't quite as strong as tippet mono, but it has the right amount of stretch and suppleness for tying--even without epoxy. Most mono thread comes in two diameters, .004 (7X) and .006 (5X). Try the larger diameter for spinning hair--the smooth finish on the thread makes the process very easy.

Most tiers prefer the finest diameter thread that is functional for their tying. The finer the thread, the less bulk on the fly. Finer threads also provide better gripping power when you tie in numerous materials. However, there are times when heavier threads are appropriate. You need to use heavy thread when spinning deer hair or when you want to add bulk to your flies. Thick thread makes it easier to build large heads on pike and saltwater flies. It can also speed up your tying by covering materials with fewer wraps. Larger thread is less likely to break from fraying, since there are more filaments. This can be important if you have rough hands or are an inexperienced tier.

Thread sizes are most often labeled using an archaic system left over from the days when silk thread was measured in zeros. For example, 000 is 3/0. The more zeros, the thinner the thread. Common thread sizes for trout flies are 8/0 for drys, 6/0 for nymphs, and 3/0 for larger flies.

The problem is that this "zero" measurement system doesn't relate to any practical form of measurement and one company's 6/0 may be smaller than another's 8/0. A more accurate measurement of both thread diameter and breaking strength is denier. This is the textile industry standard. A denier equals the gram weight of 9,000 meters of thread. Refer to to my breaking strength comparison charts to see how the different brands compare in this regard.