Choosing the Right Thread

By Scott Sanchez

Part of an article published in Fly Fishermen

After the hook, tying thread is the most important item on a fly tier's bench. In the old days, the only thread choice was silk, but today there is a variety of thread materials available in a dizzying array of sizes and configurations. Choosing the right type of thread will help you manipulate your materials better so you can consistently produce more durable and attractive flies. Without the right thread, even your best efforts can be counterproductive.

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.

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.

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.

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.
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.

Thread Brands

Danville is one of the oldest fly-tying thread companies the U.S. In reference to thread size and strengths, they are used as a standard. They also make most of the chenille you see in fly shops, and also sell mylar tinsels and braids. All Danville thread is made of nylon.
Spiderweb. This is very thin thread for tying the smallest flies. Finesse and smooth hands are necessary to use it. Available in white.

Flymaster. This is a flat fine thread and is also called Danville 6/0 or in older literature, Herb Howard Prewaxed. Flymaster is a good thread for smaller flies and where low thread buildup is critical. It is probably the most widely used thread in the world and it is the standard to which other fine threads are compared. Waxed or unwaxed; 25 colors.

3/0 Monocord. Monocord has a stiffer feel than other Danville thread. The 3/0 is good for flies larger than #12. It will work for flaring small amounts of hair, such as heads on hoppers. Waxed; 10 colors.

Flat Waxed Nylon. This is a very popular thread for saltwater flies. It has very little twist and it lays very flat. It is strong enough for hair work. The fluorescent colors are bold. Waxed; 15 colors.

A Monocord. This is a heavier version of the 3/0. It is typically used for hair work. Flat Waxed Nylon and Flymaster Plus have taken its place in the market. They have better names and colors. Waxed; 10 colors

Flymaster Plus. This is similar to Flat Waxed Nylon, but it has more twist. It is a good thread for hair and large flies. Bold colors. Waxed and unwaxed; 21 colors.

Monofilament. Ultra Fine .004 and Fine .006. Clear and smoke.

Benecchi threads are unwaxed polyester with a fair amount of twist. The twist gives it an outer texture that may help hold materials. Benecchi also has a fine GSP thread. The spools come with an end cap to hold the thread when not in use. All of the polyester threads have a similar feel. Benecchi is based in Italy.

12/0. A nice thread for small flies. It spreads out nicely when wrapped on the hook. 20 colors

10/0. A good general purpose thread for flies larger than #18. 20 colors.

8/0. A good thread for larger trout flies, bonefish flies, or flaring hair on smaller flies. 20 colors.

10/0 GSP. A fine strong thread for small flies. It is more floss-like and less stiff than other GSP threads. White.

The American company Gudebrod sells thread for fly tying and rod wrapping, as well as for the general textiles market. They also manufacture dental floss, fly-line backing and almost any filament product you can think of.

I always assumed Gudebrod thread was nylon, but Bob Siegl at Gudebrod informed me they are polyester. Gudebrod thread has more stretch than other polyesters and are a good compromise if you don't like nylon. Gudebrod thread has more wax than most, and is probably the easiest to dub on. All Gudebrod threads are flat.

Gudebrod colors are coded to the Borger Color Guide System, and spools are labeled with the thread color and the BCS number. The bright colors in this brand are very vibrant.

Since Gudebrod is in the sewing business, you can also buy this thread on larger sewing machine spools. To use this thread, you'll have to snap the spool onto a special Gudebrod plastic bobbin, or use a Griffin Multi-thread bobbin (no longer available) which fits larger spools and can be used with all sizes of Gudebrod thread.

Gudebrod also sells Kevlar and mono. The "A" rod wrapping thread can be used for flaring hair. All Gudebrod spools have built-in thread clips to keep the thread from coming off of the spool when not in use.

10/0. A very fine thread for small flies. It is the last step before going to the micro fly threads and will cover most tiers small-fly needs. It has more than twice the strength of smaller threads. 7 colors

8/0. A good thread for small to average trout flies and for larger flies where bulk is an issue. It makes small neat heads on flies. 12 colors

6/0. A thread for flies larger than #14 and for hair work on flies such as Irresistible or making small heads on deceivers. 16 colors.

3/0. A useful thread for hoppers, Muddlers, Woolly Buggers and saltwater flies. 14 colors.

G. A strong thread for hair bass bugs and also good for building heads on big flies. 13 colors.

Kevlar. The original "superthread" used for heavy hair work. 7 colors.

Mono. Available in three sizes in smoke and clear.

Gordon Griffith's
Gordon Griffith's is a tackle distributor in the U.K. All these threads are made of polyester. The 14/0 and 8/0 are similar to Benecchi thread.

Sheer Ultrafine 14/0. A small-fly thread for nymphs and drys. A good option for big flies such as salmon flies where small heads are desired. Lightly waxed; 11 colors.

Wisp Microfine 8/0. A thread for trout flies #14 and smaller. Waxed or unwaxed; 10 colors.

Cobweb 6/0
. This is a two-ply twisted thread. An option for hoppers, ribbing fly bodies, or for building heads on streamers. Waxed or unwaxed; 17 colors.

Wapsi isn't a newcomer to fly tying, but has only recently entered the thread market. Wapsi is based in the US, and also distributes many other thread brands. Wapsi Ultra Thread is nylon, and has the appearance of floss. There is almost no twist and it flattens as well as any thread available. It is similar to Danville Flat Waxed Nylon, but available in smaller sizes. It has a shiny finish and the fluorescent colors are brilliant. It is a great substitute for floss. Both sizes are identical in feel and color. It is very easy to make multiple-turn whip finishes, and it creates very smooth heads on flies. Ultra Thread is lightly waxed. Wapsi is the first thread company to actively promote denier thread sizing. Spools are marked with color and size and include a color coded end cap to hold the thread end.

UTC 70. An excellent thread for small flies and low bulk big flies. The spreading nature of the thread makes it easy to tie low-profile flies. 18 colors.

UTC 140. A great thread for flies #14 and larger. Useful for tying flies such as the Madam X, hoppers and Clousers. A good substitute for floss; 18 colors

UTC 280.
A nice flat thread for smooth heads on large flies and for tying bulky materials such as hair and wool. It makes excellent tags on steelhead flies; 10 colors.

Mono. Clear and smoke in .004 and .006.

The Canadian company Uni-Products carries the biggest range of spooled fly-tying materials. The company sells thread in a many different sizes and styles. Most of the thread is polyester, but Uni-Products also sells some nylon, kevlar, mono, and GSP threads for different applications. This company does an excellent job of labeling its products. The thread sizing labels won't peel off, and the color information is on them also. Labels in the future will also have denier weights on them.
Sizing on GSP threads has already been revamped to reflect denier weights. The 3/0 Uni-Cord is now 7/0 and the Uni-Cord 8/0 now called 12/0. Uni-Products' continuous filament, bonded threads seem proportionally stronger than other polyester threads. The unwaxed 8/0 and 6/0 feel similar to Benecchi and Griffith threads.

17/0 Trico. A fine polyester thread for tying micro flies. Finesse and smooth hands are necessary. Unwaxed; white.

8/0. An excellent thread for small flies and low bulk tying. Continuous polyester filaments are slightly bonded. The texture of the thread helps secure materials. Waxed or unwaxed; 21 colors.

6/0. This is a heavier version of the 8/0. An abrasion-resistant thread. Good for big drys, bead-heads and streamers that require tying in multiple materials. Waxed or unwaxed; 24 colors.

3/0. A flat polyester multifilament thread that works well for covering bulky materials. Used for flies larger than #12. Waxed or unwaxed; 17 colors

A+. A heavier version of the 3/0. It can be used for hair bugs and building bulk on flies. Waxed and unwaxed; 13 colors.

Big Fly Thread. A heavy, flat, bonded, polyester thread with continous fibers. Good for bass bugs if you desire a non-stretch thread that isn't slippery like GSP or kevlar. Useful for building bulk and covering material on pike and offshore flies. Unwaxed; 10 colors.

1/0 Neon Flo. A very bright fluorescent 2-ply polyester thread. Designed to make bright heads. Also good for thread bodies and ribs. Unwaxed; 6 colors.

2/0 Poly II. A 2-ply polyester thread for those who prefer a traditional round tying thread. Unwaxed; 12 colors

Uni-Cord 7/0. A heavy duty thread for flaring hair, wool, and egg yarn. A great thread to use with large quantities of hair and for marginal hair. Uni-Cord has a nicer finish than some other GSP threads. Unwaxed; 6 colors

Uni-Cord 12/0. A finer version of the Uni-Cord 7/0. A good option when you need superior strength on small flies. Unwaxed; 6 colors

Kevlar. Similar in size to other Kevlar, but it has a much softer feel. Natural yellow color.

Uni-Mono. Three sizes; clear.

* This chart is a list of the options sold by various thread wholesalers. Some information is derived from manufacturers' data, and some from personal experience. The thread comparison chart was compiled by verifying the information supplied by the thread suppliers, conducting thread breaking strength test with a Chatillion scale, using loupes with 8X - 20 X magnification, feel, and tying experience.

True diameter comparisons are very difficult with thread because it compresses when a standard micrometer is applied to it. I have tried to mic thread, and my results varied as much as .003" on a single thread. That is too much of a variable to me.

The most accurate of available measurements is denier. This is the textile industry standard. A denier equals the gram weight of 9,000 meters of thread. Since nylon and polyester are comparable strengths and weights, denier is a fairly accurate comparison.

Wapsi was the first to actively promote a denier thread designation. They conducted tests of various threads both in-house and at a private lab. They gave me permission to use the results in this article.

GSP is lighter in weight than other materials, so the denier weight is lighter than the strength and appearance would indicate. Twisted ply thread on the other hand, seems to be a heavier denier for a given strength. From this I conclude that twisting fibers adds more weight within a given length of thread, but it does not add strength.

Jean-Guy Cote of Uni also provided denier and breaking strength results for his thread, and Gudebrod also supplied breaking strengths. On threads where the denier was not supplied, I compared them against threads of known denier by visually inspecting at magnification, by tying with them, and using a non-caliper tippet gauge.

The tippet gauge was a slot type made by Gage.It. On this tippet gauge, you push the material into the slot until it touches the sides. Thread compresses so I didn't use this for accurate measurements, but I used it to get a rough idea of comparative thickness. I did this by pulling the thread into the gauge six times and comparing the average. While compiling this information, I tied the same fly, in the same size with various threads. I felt this would give me a real life comparison. Mono thread was measured with a micrometer. Both Gudebrod and Uni have a larger mono thread. I didn't have samples before I finished the article so they are not on the charts

While conducting breaking strength test, it occurred to me "if nylon and polyester are comparable strengths, breaking strength should give a fair approximation of thread sizes." Above I list thread by types of use, and my opinion of diameters within a category. Even among the best thread producers, thread strengths and diameters vary. These charts were designed to give you a fair comparison and not exact scientific results.

Since thread selection is part education and personal preference, I thought I would leave you with the thread favorites of some of the people I feel are expert fly tiers.

Chris Helm (the bass bug guru)
. Helm likes heavy GSP threads for hair bugs. For other flies, he prefers Gudebrod. He also likes the new Wapsi threads in some situations.

Tom Travis (spring creek guide and Orvis contract tier). Travis has used Uni 8/0 since it first became available. He likes the consistent colors, but he can't live with out Fly Master in light olive and coffee. On very small flies he uses Benecchi 12/0. On saltwater flies he likes fine mono thread in conjunction with epoxy.

Johnny Boyd (owner of Montana Tie'm and contract tier for Frontier Flies). He likes Gudebrod in all sizes. It is flat, waxed and strong.

Marv Nolte (premier Atlantic salmon fly tier). Nolte owns 500 spools of Danville 6/0. He prefers it over all other threads because it lays flat and he is familiar with it. The stretch in the nylon tells him when to back off to prevent breakage, and he knows exactly how much room a few wraps takes.

Brandt Oswald (precise tier and outdoor writer). Oswald likes Danville Flymaster. He likes the stretch, the fact that it builds up slowly, and the color range. He is also impressed with Wapsi Ultra thread. The 70 denier is similar to Flymaster and the fluorescent colors are gorgeous.

Scott Sanchez (author of this article). On spring creek flies, I like 10/0 and 8/0 Gudebrod. For most average size trout flies, I use 8/0 Uni, and I can't live without Rusty Brown. I also use red Wapsi 70 for "Royal" fly patterns and chartreuse for flies of that color. For hoppers, Madam X and big nymphs, I use Gudebrod 3/0 or Wapsi 140 depending on color. For bonefish flies, I like good old Danville 3/0 Monocord. It is the right size and has the correct colors. On bass bugs, I use Gudebrod "G" or Danville's Flymaster Plus and if I have marginal hair, I resort to Uni-cord. Overall, my preference is flat, waxed and with a little stretch.